you've seen collies trained as protection dogs? or just the nervy, nasty, snappy types? I wouldn't want that trait in any dog, not a chance!! some of the collies I've seen are proper unpredictable, they're sort of half cowering and you never know when the fookin things are going to snap.
No, not seen Collies trained a PPD, just one's that were not afraid to bite.
If you look on Youtube there are Boxers, Labs and all sorts of trained biters.
There is a fellow that I've used for training bite work, that has Springer trained to the sleeve and it's a proper maniac.