If the snails are being bothered, they may simply be in a defensive mode and not moving. Not sure what species of dottyback you have but as clown will not normally molest a snail. Snails are also quite sensitive to changes in water so it would help to know how you acclimated them to your tank. Anything other than a slow drip acclimation might have been a shock to them. I've also had snails that simply stay put for several hours and then begin to move, so you may see them relocate after a night in your tank.