Best Deterrent Spikes for Fence Tops (What to Look For and What to Avoid)

The best deterrent spikes for fence tops are ones with irregular, staggered spike heights — not flat single-height strips. Flat spikes stop birds from landing but let squirrels, cats and foxes walk straight over them; staggered heights disrupt the footing of climbing animals as well. You also need a strip that wraps the top of the fence on multiple sides, not just sits flat on one face.

Why most cheap fence spikes fail within a season

Walk down any garden centre aisle and you'll find flat plastic spike strips for a few pounds. They work, briefly, for pigeons on a clean horizontal surface. But they fail in three ways that matter on a fence top:

They sit flat. A fence top isn't just a horizontal surface — it has two faces and a top edge. A flat strip covers one face. A pigeon or squirrel simply moves to the other side.

The spike height is uniform. Single-height spikes are easy for squirrels, foxes and cats to navigate. These animals don't approach a surface the way a pigeon does — they step across it. A consistent spike height becomes a known obstacle they step over or between.

The plastic goes brittle. Most cheap spikes are made from recycled or mixed polypropylene with minimal UV stabilisation. After one UK winter — freeze, thaw, UV, repeat — they snap when you brush against them. You end up with broken spikes that deter nothing and look worse than nothing.

What the spike design actually needs to do

A fence top spike strip needs to solve three separate problems simultaneously:

1. Stop birds landing — the spike points need to be close enough together and tall enough that a pigeon can't find a flat foothold.
2. Stop climbing animals crossing — the spike heights need to be irregular so animals can't step confidently between them. A squirrel or fox testing a uniform spike row quickly works out the rhythm; irregular heights remove that predictability.
3. Cover the whole fence top — including the two side faces, not just the horizontal cap. This means the strip needs to fold or wrap, not lie flat.

ThornGuard spikes are designed around exactly this problem. The strip uses three spike heights — 12mm, 22mm and 36mm — in an irregular pattern. The shorter spikes catch birds; the taller, staggered spikes disrupt the footing of anything trying to walk across. The strip also folds along its length, so it wraps a fence top and covers both faces as well as the horizontal surface — three sides from one strip. You can read more about fitting on the ThornGuard fitting guide.

How to measure your fence and work out how many strips you need

Measure the total run of fencing you want to protect in metres. Then decide whether you're fitting to just the top cap of the fence or wrapping it around the top edge and down both faces.

• Top cap only (flat): one strip covers 0.4m per strip (ThornGuard strips are 400mm each).
• Wrapped three-side: splitting the strip lengthways roughly triples the run — one strip covers the top and both sides of about 0.4m of fence, but you can also split sections to cover a longer run at reduced width.

ThornGuard comes in a 4m pack (10 strips) and an 8m pack (20 strips). Because the strips can be split lengthways, a 4m pack can cover up to around 12m of fence top when used in split configuration.

For a standard 6-panel fence (roughly 10–12m run), the 4m pack in split configuration is usually enough for the top cap. If you're wrapping all three sides fully, go for the 8m pack.

Fixing methods: screws, cable ties or adhesive

The right fixing depends on your fence material:

Timber fence tops are the easiest. Pre-drill and screw directly through the strip's base channels into the wood. This is the most secure long-term fix and what we'd recommend wherever you can drill. Screws are included in every ThornGuard pack.

Gravel boards and capped fence panels work well with cable ties fed through the base of the strip and around the fence cap. Also included in every pack. This is faster than screwing and still holds well.

Concrete or composite capping — if you can't or don't want to drill, waterproof adhesive pads (sold separately) bond the base of the strip to the surface. Clean the surface first with isopropyl alcohol, press firmly, and allow 24 hours before exposing to rain. Full prep guidance is on the fitting guide.

If your fence posts have a different profile to your fence panels — which is common on close-board fencing — cut a strip to length to cover the post cap separately.

Does the fence height matter?

Yes, but not for the reason most people assume. Deterrent spikes don't stop a fox from jumping over a fence — a determined fox can clear 1.8m from a standing start. Spikes on a fence top work by making the landing zone too uncomfortable to use as a crossing point. A fox's usual method is to put its front paws on top of the fence, test the surface, and pull itself over; spikes interrupt that test. The same is true of cats.

For fences under 1.5m, spikes alone may not be enough for a determined fox — consider combining them with an angled topper or roller bar above the spike line. For standard 1.8m close-board garden fencing, spikes on the top are effective against both casual climbers and birds.

Squirrels are the trickiest case because they can launch from trees, sheds and overhanging branches. If you have a squirrel problem, spikes on the fence top help but you should also identify what they're launching from. We've covered this in detail in how to stop squirrels climbing your fence.

What about fence posts specifically?

Fence posts are a separate problem. Birds — particularly pigeons and crows — use fence posts as perches far more than they use the fence run itself, because posts offer an elevated clear view. Flat fence-top strips don't cover posts well; a post cap is usually square or round, not the same profile as a flat fence panel.

Because ThornGuard strips fold, they can be wrapped around a square post cap to cover all four faces, or cut to fit a smaller surface. This is one of the practical differences between a flexible folding strip and a rigid flat strip — the latter simply can't conform to a post shape.

Common questions

Do deterrent spikes work on squirrels as well as birds?

Flat single-height spikes do not reliably stop squirrels — they step between the spikes or push them aside. Spikes with staggered heights (such as 12mm, 22mm and 36mm) disrupt footing and are much more effective. Combining fence spikes with removing nearby launch points (overhanging branches, adjacent sheds) gives the best results.

Are fence-top spikes legal in the UK?

Yes. You can fit deterrent spikes to your own fence, wall or property without any special permission. The only restriction is that spikes must be genuinely deterrent — they should not injure animals. Humane plastic deterrent spikes are completely legal. For more detail, including rules on party walls and rented properties, see our full guide on whether bird spikes are legal in the UK.

How long do plastic fence spikes last outdoors?

This depends almost entirely on the plastic grade. Spikes made from recycled or unspecified polypropylene typically go brittle after one or two winters and snap. Spikes made from UV-stabilised virgin polypropylene — the grade ThornGuard uses — resist UV degradation and freeze-thaw cycles significantly better, lasting several years under normal UK outdoor conditions.