You could use clumping bamboo, very important: CLUMPING, not running.

I also recommend posting to the Florida Gardening forum in gardenweb.

Maybe you could instead offer to pay to have the tree removed, and suggest he install a metal pole to tether his dog? I bet the cost to remove the tree is partly his reason for not taking it out. A 25 foot tall screen is certainly possible, but on the south side, is your pool close to the property line so that it would be subject to leaf droppage and shading that you may not want?

Some plants suitable for screening in warmer zone 9 conditions here in California might include Schefflera pueckleri, Strelitzia nicolai, Podocarpus gracilior, and various Pittosporum species. I am sure there are a whole range of other plants used for fast evergreen screens in Florida. Bamboos can also work, but they can be extremely messy around pools, as they are always shedding leaves. You might consider some palm species such as Chamaedorea or Rhapis as well, they don't shed, and grow vertically rather than horizontally.