Helium filled balloons tied to weights in pool. If you want to create the illusion of floating balloons use fishing line which is virtually invisible. (IDEA- Could also ADD some glow sticks so that the balloons GLOW over the Pool at NIGHT!
Here are The Animal Rescue Site, we pride ourselves on our level of cat craziness and believe you should, too. Scroll down to find out if your feline fanaticism qualifies you to join the Crazy Cat Lady Club!