How do I prevent salmon sticking to the BBQ grill?
If you don't fancy cooking in aluminium foil (kind of takes the point away), you need to make sure you have a super clean, extremely hot grill. 

Why?

Clean (No tasty burnt fat from the burgers), flesh sticks like #### to a blanket. You can get away with it when cooking steaks because they are just so much stronger. So get a wire brush and clean an area for fish cooking and keep it clean :).

Hot, as hot as you can pretty much. You want the second that Salmon (or other fish) hits the grill for it to blacken. It'll help make sure the flesh is no longer 'fleshy' and again less likely to stick. Don't try lifting it till' you know that underside is like a pink and black Zebra on it's underside (3-4 min).

When it does come to lifting you could really do with a nice sharp fish slice, not a blunt fat ended egg slice. 

Good luck.