Slugs and sharp gravel - does it work as a deterrent?

No.

Maybe.

But no.

Can you spot the slug?

Slugs seem to be able to cross anything - I've even seen them walking up the netting pictured. Gravel doesn't seem impassable to them, although they may not like it. 

As one of a series of measures it may help - but does it act like a barrier that slugs are unable to cross? Categorically no. 

Next experiment will be copper tape. After that - sticky back velcro.