Now, since you already have it, the best you can do:
- Fence the pool. It's almost a must, no matter the tenants have kids or not... what if they have a party and small kids come to play?
- Hire a professional and maintain the pool (and charge the tenant). If you don't, if the tenant does not maintain it, before long, your pool will be effectively destroyed and become unusable. You'll have to fill it with mud or it will cost you a fortune to repair and restore it.
- Buy umbrella insurance coverage
On the other hand, filling it now may not be a bad idea, especially you plan to hold the rental property for 10-15 years.