Can Vegas' be combined with cs Shield/Protect?

Let's say I want to scroll a staff with a 10% scroll but also use a vega (making it 30%), plus use a shield/protect on it so the slot doesn't go with a fail and a guardian* scroll if there's a fail. Is this possible? If so, how would it work? I remember trying this with a vega+Pam thong but I couldn't get it to work (perhaps I was doing something wrong). Thanks for the help!

edit: I meant to say 'Guardian' instead of 'Protect' in the title. My bad.