Adding to what agalisgv said, I have a pool in my backyard. The yard is pretty inaccessible to young children. All the walls are at least six-feet high, plus have high trees and bushes that would be extremely diffcult for anyone to get through. From the driveway, you would have to go through two gates, each with latches that are five-feet off the ground.
When I bought my house, the pool came with a mesh fence. It is a complete eyesore. The pool is a very unusual shape and dominates my small backyard so having a four-foot high fence surrounding the pool basically means you look out my windows and see the mesh fence. Still, I have left the fence up. However, one piece tore and I cannot find a matching piece (the fence comes in parts that each have three mesh screens and must fit the existing holes poured in the concrete). A new fence would probably cost at least $1,000.
The other thing about the fence is that opening it up to actually use the pool is a bitch. you have to force the fence out of one of the holes (it doesn't have a gate). Some of the newer fences have "gate" pieces, but those pieces alone seem to run more than $300.
Given that I have no children, none of my family members or friends bring children to my house, and it is virtually impossible for a child to access my yard, I don't see why a pool fence is necessary. According to the CDC, between 1999 and 2007, the rate of swimming pool drowning deaths was 0.3 per 100,000. That is 3 out of 1 million. The Consumer Product Safety Commission's 2010 report indicates that there are about 4,200 submersion "incidents" annually in the US, with about 385 deaths among children under the age of 15. Appoximately half of the incidents and 3/4 of the fatalities occur at private residences as opposed to public facilities. Of the fatalities, 46% occurred at the victim's own home and 22% occurred at the home of a family member or friend. Only 5% of the deaths were reported as occurring at a neighbor's home.
From that data, I think the odds of one of my neighbor's children entering my yard and dying in my pool is .00000015 or 1.5 out of 10 million. I think I have better odds of being killed by lightning.