PEAKTOW PTS0002 Heavy Duty Universal Adjustable Coupler Lock Trailer Hitch Storage Security Lock Fits 1-7/8, 2, 2-5/16 Inches Couplers

We use this guy, Reese branded, as a deterrent. You could follow up with wheel lock too if you're in an area of concern. When we park ours, I stack wood etc around the trailer so you'd have to move it all to steal it without damaging it. coupler lock