Speak to whatever little shit they send. Have someone conspicuously video tape you. Tell them that they are NOT welcome on your property and that any further contact will be treated as trespass and/or criminal harassment and that all activity on the property is being recorded. Follow it up with a registered letter stating the same thing.

If the shits come on your property again, get it on tape — if the cops are useless as tits on a boar, you can always speak to someone from the D.A.’s office directly and short-circuit the process of filing charges.