In UK I gather you're allowed anti-climb paint - which damages clothes - to prevent unauthorised access (trespass, say); but you're not allowed glass or spikes which damage people too. People usually signpost use of deterrents, I'm not sure that's a requirement, probably just part of the deterrent.
So there's certainly precedent for damaging others property to hinder "trespass".
You're generally allowed ultra-sonic devices like cat scarers that deter people's pets from gaining access to your property, and whose effects impinge across property boundaries.
So I reckon as long as you signpost "ultra-sonic deterrent" then the onus is on those who're infringing your privacy and peaceful enjoyment of your property to avoid any potential damage by avoiding your property.
In UK I gather you're allowed anti-climb paint - which damages clothes - to prevent unauthorised access (trespass, say); but you're not allowed glass or spikes which damage people too. People usually signpost use of deterrents, I'm not sure that's a requirement, probably just part of the deterrent.
So there's certainly precedent for damaging others property to hinder "trespass".
You're generally allowed ultra-sonic devices like cat scarers that deter people's pets from gaining access to your property, and whose effects impinge across property boundaries.
So I reckon as long as you signpost "ultra-sonic deterrent" then the onus is on those who're infringing your privacy and peaceful enjoyment of your property to avoid any potential damage by avoiding your property.
Aside: Not sure how far the law has come but there are guidelines from CAA saying not within 50m of another person, not within 150m of built-up areas (eg https://publications.parliament.uk/pa/ld201415/ldselect/ldeu...).