Like Grif said, the divider needs to be secured in the tank, not just sat on the substrate... But IMO you should get a new small tank for the snails and remove them completely from your frog's habitat. Even if the snails aren't toxic to you, they are constantly secreting mucus from their skin that may be harmful to your frog. Snails and slugs can be highly toxic to reptiles and amphibians, especially if they do not naturally exist in the same area. All frogs also secrete toxins from their skin which can be harmful to other animals.
It's a bad idea to keep two species that both secrete toxins together, especially since both of them can also absorb toxins through their skin. With that setup, there's no way you'll be able to go the entire life of your animals without ever having cross-contamination. If I were you I'd remove the snails and the bedding and sterilize the whole tank just to be safe.

Not trying to nag, you definitely want to deal with the tox problem first! Just thought I'd mention it. I've had a snake get very ill and regurgitate just from eating a pinky that I had offered to my frog, and heard several horror stories of people feeding snail-eating animals the incorrect species.