Sorry, but the solution that is going to cause the least headache for you is to just bite the bullet and get a different kind of filter if you want to go with sand.
Marine aquariums certainly dont use undergravel filters. I think what you're referring to are "gravel tidy's" and they are for holding stuff in place rather than holding it away from something else and they certainly dont work with sand.
The answer to this one is very clear cut, if you feel you need sand for your cories then you need an internal box filter or better instead of a UGF
hes right, as far as im aware, UGFs cannot function with sand, or i guess they would be called under sand filters even with a gravel tidy, i dont think water would be able to be pulled through the sand.
I'd get rid one or the other, If i was you i would get an internal pump if you want to keep sand in your tank but sand can be messy anyway.I'D HAVE GRAVEL
Tanks evreyone I now agree so its rounded gravel for me and evreyone is saying don't get it and there is a down side as well so thanks for saving my time and money