If you are okay with him having baling twine, use baling twine to tie milk jugs or laundry detergent jugs (washed off of course) anywhere you can tie them. I had problems with the two steers we are raising taking their water heater out of the water, flinging it around, and letting it burn up in the straw. They love the milk jugs, they can mouth them, rub on them, fling them around. And there is always baling twine around to re tie them. Plus it is a great use for milk jugs, and when they are too crumpled or destroyed to be fun, they go in the recycling bin.
If you are a little leery using baling twine, a lead rope (if it will fit through the handle) also works well. That is how I tie up jolly balls for the horses.