You didn't say what age your children are, but with small children you MUST have positive control over access. It sounds like that means a fence, in your location.

Regarding a latter, you probably want to keep in mind that it's not just a way IN to the pool, it's also a way OUT. I'd be afraid to remove a ladder for that reason, even more than for the sake of the liner.

You might want to look through the AG photo gallery -- it's far from comprehensive, but you might get some ideas. However, I don't really thing rock added AFTER the pool is up and filled is going to migrate under the liner.