I do not practice law in your state, so anything I say is only general information and you should consult with an attorney in your area before acting. It appears that you ahve no interest in trying to maintain good relations with this neighbor, so it's time for a cease and desist letter to be sent certified telling the owners of this property that they are not to continue trespassing on your land for ANy reason. and this includes: (list it, including their taking or "borrowing" your stuff without permission, coming on to your land to maintian their property and putting a get to open onto your property. If they ignore the letter, then you need to file suit to enjoin them from continuing to do it and possibly add a nuisance suit and civil trespass and possibly ask for damages if they've cost you anything, including if your property value is harmed from the placement of their gate/stepping stoned, etc... Your peace of mind is absloutely worth a 30 minute or 1 hour consultation with an attorney and it may be wise to let the attorney handle the whole thing. Have you contacted the police about any of this and asked the police to give a verbal trespass warning? In some instances that stops thoughtless behavior, but it seems this is much more than inconsideratemenss.
This is not intended to be legal advice or create an attorney-client relationship. If more information is needed, you should consult with an attorney in your state regarding the specifics of your situation and the options available to you.