make an anonymous tip that you suspect a meth lab is across the street
kidding of course.....
a-hole neighbors suck, write down every encounter you can think of, how/when you've used your garage etc....maybe get a written statement from your other good neighbors on the "situation".......i've been pretty fortunate so can't offer you firsthand experience, just what i've read and heard.
if i'm correct what they are doing is harassing you, which will work in your favor down the road if it's documented, there have been others on the bbs who have had similar situations with neighbors messing with trees and such.....i'm sure they'll chime in.