I use tiles rather than slate. You can find tiles as small as one square inch and 1/4 inch thich and up. (I have a 12x12x1 tile that weighs a few pounds used to hold down a large log.)
You can get a glass and tile drill bit to make the hole in the tile- much easier to drill than slate- just be sure to score the tile where you want to drill the hole or the bit will slide around rather than bite. Because I do heavily planted tanks, I want to be able to plant right up to the edge of the wood and not have a shallow tile/slate impede root growth.
I use two techniques to help with this. I want as much wood as possible showing- ie not buried- and I want to have the hold down tile on the bottom glass. To do this I use nylon spacers which I get the same place I buy SS screws. I use a screw long enough to go through the tile, through the spacer (or spacers if more than one is used) and into the wood. Secondly, because this insures the max amount of gravel between the tile and wood for hold down help, I can also minimize the size of the tile neeeded to do the job.
You can get a glass and tile drill bit to make the hole in the tile- much easier to drill than slate- just be sure to score the tile where you want to drill the hole or the bit will slide around rather than bite. Because I do heavily planted tanks, I want to be able to plant right up to the edge of the wood and not have a shallow tile/slate impede root growth.
I use two techniques to help with this. I want as much wood as possible showing- ie not buried- and I want to have the hold down tile on the bottom glass. To do this I use nylon spacers which I get the same place I buy SS screws. I use a screw long enough to go through the tile, through the spacer (or spacers if more than one is used) and into the wood. Secondly, because this insures the max amount of gravel between the tile and wood for hold down help, I can also minimize the size of the tile neeeded to do the job.
