Legal Question in Real Estate Law in Washington

In such a situation as this, I often advise my clients to do the following, which usually takes care of the issue: Offer to hire a surveyor to demarcate the property boundary between both lots. Offer to have someone they agree to as well, so that they can trust in the result. You then want a contract that states that although you will pay the surveyor up front, if it turns out that you are correct, in that their property line is behind the fence, and that they have no right to hang this plastic fence on your fence, then they will reimburse you 100% for the surveyor's cost.

If they want no part of it, then unfortunately, your only real option is to sue them for a declaratory judgment, wherein you ask a judge to adopt a surveyor's report that demarcates the line between your properties. You will want to ask for attorney's fees in that process, and you may get them, but do not count on it. It can be expensive and time consuming as well. Hopefully, for your sake, they will agree to the first option and you guys can then go on living in peace.