When my daughter was in a home daycare, they decided to install an inground pool. They told us they were putting up a fence, but then decided not to. Luckily, I was already pregnant with my second child and was leaving before it's completion, because I would have been pulling my daughter out of there for that very reason alone. They had a sliding door to their backyard that her older children could open. It takes one second for a child to slip out the door and into the pool. Too much of a liability in my eyes. Definitely get it fenced before opening up.
With that being said our current home we bought only a few years ago had an above ground pool and I did run my daycare here last summer. It was attached to our back deck and was gated off. The children were not allowed on the deck and no toys were allowed near it on the grass. However, my husband and I decided that it was too much of a liability with our children being so young, and having the daycare that we tore it down at the end of the summer. So no more pool. Not saying you have to go to our extreme, but parents like to know that I had rules in place along with the gate.