I also think it would be appropriate to provide some additional barrier on the pool itself, such as a locking ladder, signs saying "No Tresspassing - Violators Will Be Prosecuted" or something like that. Got a dog in the back yard?

There is a doctrine in civil liability which deals with minors and "attractive nuisance" items on your property, basically stating that ...if you build it, they will come. So, you need to do EVERYTHING to show that you tried to avoid the possibility of injury, even if they tresspass.

We are lucky enough to live in the country, but have relatives living close enough for their grandchildren to wander over occassionally - we have a locking ladder which will work for now as they are young.