I tried the stickers to begin with, but they always became unstuck after a while no matter how well I applied them. That might be because the bottom of the tub isn't completely flat; it has a slight diamond-patterned texture. I suppose without that it would be even more slippery on its own, but it seems more of a drawback to me.

I don't recall ever seeing cassette players at the Goodwills here. But I wasn't looking for them then, so that's not a bad idea to check.