I had a spare cheapie cork bulletin board from Costco so I've commandeered it for blocking. It's 2' X 3'. I suppose I could take a permanent marker and make a grid on it. The cork isn't affected by dampness and the frame is ?aluminum? and plastic, so I'm ok there too.
Some people pin items to their rugs, but a) my carpets are not that clean b) I don't have that much floor space and c) I don't really want a wet carpet.
I just put the bulletin board across my tub and if I need to shower, I put it up resting one side on the shower curtain rod and the other on the lip of the shower wall.