Write your pool rules on the sandwich boards. These rules should include prohibitions against running, diving and horseplay. Write in large capital letters that are easily legible from a distance.
Punch a couple of holes in the top of each sandwich board with a drill. Make the holes large enough that a shower curtain ring will slide through the hole with no resistance.
Lay two boards back to back and join them together with the shower curtain rings. Make enough of these double-sided rules signs that people see them immediately upon entering the pool grounds.
Install the safety signs at each pool entrance. Prop them up like a wet floor sign on level ground. Don't obstruct exits or walking paths.
Stencil the water depth along the sides of the pool in a contrasting paint color. Space the markings at equal distances and be sure that you clearly indicate the shallow and deep areas.