Frogs return to ponds each February or March to lay their frogspawn and then most of them disappear, just as quickly as they arrive! The timing depends on the weather and the actual location.
Frogs spend the majority of their time on dry land, under stones or in a damp cool spot in your garden. They use ponds at spawning time to lay their frogspawn, but need to be on land to feed. If the frogs cannot escape because your pond has steep sides and a low water level, or pavings that overhang into the pond then they will die. You must make provision for them to escape.