My 21 month old son has realized that he can lift the air vent registers and toss his toys into the "abyss"... Anyone have any suggestions for a proper way to secure them?
Double sided tape?
You could drill a hole in each end of the register where it overlaps the floor, and drive a pan-head screw through it into the floor.
If you don't want to drill into your floor (whether it's wood, laminate or other), clear caulk can do the trick - but it needs time to cure.