Ditto what Rondo said. I'm finding when I put them in when the tires are hot, in just an hour or two they are almost ready to fall out. Once retightened they stay tight, though.
Grampachet, I once turned one of those BAL chocks sideways between tires when I forgot to remove them.
Acutally, both sides. I was very concerned about damaging the tires but was able to carefully back up and then remove them. The tires seemed not to be hurt, or at least over time they seemed to be fine.