maybe the kiddie-floaty like things (or the adult versions) in case the dog fells into water, then he may have something to hold onto/get on it. Also maybe some wooden slabs (plastics would be cheaper but would not look good, and they may even fly away in strong winds, but handling wooden slabs maybe harder because of weight, may be a 2 person task to take them on and off) cut to shape of your pool to cover it completely/partially. This will reduce the chances of doggy unknowingly (that is to you guys would know if it is risky for him to go outside or not) fall in the pool. This will also double up as ypour general pool cover to keep your pool water clean, and can also help you insulate your water better, in case you live in a frigid climate and heat the pool, or in some very hot climate and want to keep your water cool.