Club head slipping off shaft

STOP
Dont waste your money on new clubs.
99 times out of a 100, the heads are NOT slipping off.
If you want to check, stand the clubs up in a line, they should all be 1/2 in difference in length from 5-6 or 3-4 and so on.
If the heads have come loose, you will see the difference in length of overall club.
As has been said before, the ferrule has just moved up the shaft, not the head moving down.
Take the lid off your kettle and place the ferrule into the steam for a few seconds. Then, using a rag, push the ferrule down against the head. Job done and a huge saving on a new set of irons.
HTH