Wow, I got this question a lot more than expected. What I have been using is a med/fast curing epoxy I buy from a great guy in the aviation business. It is designed to be very viscous, almost like rod finish, but sets in a few hours, or about 45 mins if you use the fast cure option. The trick I have found is to leave to cuts fairly rough in the bottom, the finish will soak in quite a bit, so you may have to add a bit to it as you go. I have never had one pop out. Another option, if you just want a solid color or two, is to use ship deck caulking. several companies make it, it cures really slow, bonds like crazy, and has a very "tactile" feel to it. It is VERY sticky and messy, but it will never come out! I hink you can get it in black, white, brown and a mahogany color. Hope that helps. I am sure there are other options as well.