Slipped roof tiles 2

[woodchopper]

A few tiles on the edge row of my garage have slipped down and taken the cement that fills the gap/holds them in place along with them - I can push them back up but a few months later they are back down again - should the tiles not be fixed in place to prevent them from slipping ?
I always thought tiles were placed along batons on the joists to stop this from happening ?

[dustypuss]

i f you have a mastic gun squeeze a little mastic under each tile to stick them together bit of a botch job but it might bye you some time.