The DUI statute in Washington is clear that you must drive a vehicle "within this state" to be charged with DUI; however, operating a vehicle on your property, even while intoxicated, has been adjudicated and there is precedent on the matter. The situation would really depend upon the circumstances of your case, for instance, were you near a public road or did you have immediate access to a roadway. This scenario would require discussion and analysis of the facts, but there have been circumstances where operating a vehicle on your own property, even if intoxicated, has been determined to be up to the property owner's discretion.
One of the typical elements of such a charge is operation in or on a public way. You need to check with the local criminal statute for the specific application.
Police generally can cite soemone for a moving violation in an "area where the public has a right to travel". These can be quasi-private roads that have access to the public right of way.