That is an alternative, but fish could also eat the eggs as well. You may be better removing any leech you find, and keeping the frog/toad spawn in a terrarium until they start to hatch, when it will be safe to move them back outside, as they can evade predators at that stage. What species are the frogs anyways, and do you have any pictures of them? Don't be afraid to post pictures, we love frogs here!