A piece of marble is not outrageous. How about buying one (or two shorter ones) off-the-shelf and installing it (set it in thinset for safety), then caulk the edges? Tilt it inward a bit when you set it.

Or maybe go to a tile shop and ask for one that's damaged or discontinued for a cheaper price.

Or paint it with Mapei aquadefense and leave it alone.

My concern with a piece of stone adhered with thinset is that the removal of the stone in the future will cause some damage.

I like the idea of a waterproofing membrane. I have some leftover Hydroban. Not sure if it will work as a waterproofing barrier for a couple of years without any tile on top of it. I will contact Laticrete to find out.

one thing about the Hydroban-- if, when pulling the temporary curb, you damage the memnbrane, you can paint some more hydroban on it, and you're just as good as new.

Bill,

Any thoughts on whether Hydroban left exposed on the top of the curb will work for a couple of years?

If exposed Hydroban won't work, could I get away with installing a cheap solid piece using silicone or something like silicone that would make removal easier? More than pulling off the hydroban, I'm worried that large chunks of thinset and maybe even the vertical portions of the curb I want to keep will come out at the time of removal.