You could use an old 2×4 or cinder block as a wheel stop. But they always slide and you never have them when you need them.
If you routinely haul a boat, camper, or other utility trailers, you need to have these in your rig.
The Haul-Master Rubber Wheel Chock With Eyebolt will ensure that your trucks and trailers will stay in place during storage or while you are working on them. It provides maximum all-weather holding power for trucks, trailers, and cars during maintenance, loading, or emergency. The stepped face and textured base provide a firm grip to lock the chock in place using pressure from the wheel. The eyebolt can be used to link two chocks together or attach to a chain to prevent theft.
Don’t be the guy whose trailer gets away!