I was going to try to build mechanical surge brakes for my heavy trailer (like boat trailer brakes). But never got them connected up. The trailer wheels have the original coaster brakes which should work. Or disc brakes could be built.

But after starting to use the trailer, I concluded that they just aren't that important (for my needs).

When empty, I can stop.
When fully loaded, I don't go too fast on the level.
Descending fully loaded might be one time when they might be helpful, but I don't think I've ever had to do an emergency stop on the two hills that I regularly go over.