[unclebilly]

I saw a pretty slick setup.

Take a piece of 6"square tibibg, drill a 1" hole in it in about the middle.

Take a trailer ball that fits your tongue, drill a hole through the threaded bolt big enough for a pad lock.

So what you do is you put the ball in the tongue and close it per normal, then slide the square tubing over the tongue and lift it up so the trailer ball sticks through the hole drilled in step 1. Put a pad lock through the hole in the ball spigot (bolt?) and lock it.

Pretty hard to hook onto now.

My dad's boat trailer got stolen once, the next one he built had a chasin link on a wheel on each side. There was also a short length of chain welded to the frame with a hook to hang it. The idea was that when the trailer was parked, the wheels could be chained with a padlock so they couldn't turn far.