DEAR ERIC: Can you offer any advice about a good friend who lets her dog jump in my pool? I have an in-ground vinyl liner pool so one concern is the dog could damage the liner with its nails or teeth.

We’d never had a pool before, but the house came with one, which was part of its appeal, at least in my eyes. We were in our early thirties then, with two children—Molly, four, and Jordan, two—and we ...