No, there is no right to access another person's property in the alleged event of fire. After all, if you had a fence not on the property line but fully withing your property, he'd have no right to go and cut a gate into your fence simply because he wants an additional eggress; the same principal applies--your property is your property, and he has no right to acces your property.That said, if he has sole ownership or control over the fence, he can put a gate in it, the same as he could tear it down. That still doesn't give him a right to access your land: whether there is a fence or not, gate or not, etc. it is your land.If he dumps on your land, call the police. If he or guests trespass, call police. If you like, put a small fence around or in front of the gate/eggress, one that is solely on your land (100% under your control) to block anyone from coming through. And/or set up a video camera to capture dumping or trespass and use that when you call the police.