Trespassers

If there is no right of way or other legal right of access to your land, a person going onto a property you own or rent without either express or implied permission is technically trespassing.

However, trespass, except in certain very specific circumstances, is not a criminal offence. It is a tort - that is, a civil wrong - and unless you can prove real damage to your property, suing that person would probably only recover nominal damages.