normally i just placed it on gaps at rocks ( low flow ) and wont drop .
sometimes mine keep dropping like 10 times when the flow is high. super frustrated !
the glue, just apply and place ( hold for 5 seconds or more let it harden awhile first else fly off )
the 2 have to mix 1 is call epoxy ! will make skimmer go crazy one. i prefer glue over epoxy. neater and less messy for me