yeah mullet is alright, prefer yakkas or fresh squid though. poddies are great for certian things, theyre supposidly alright for jewfish.
in regards to your line breaking, what reel are you using (how much line capacity), how old is your 50 lbs leader (is it off?), what knot are you using?
if it keeps happening get some nylon 100lbs wire, crimped, 8/0 circle, slab of mullet.
my experince with rays is they just go screaming off, absolute nucense, sharks take a bit of a more slower, controlled, even run, just head down and pull. Sometimes, rays stick themselves to the bottom and won't come up, just keep the pressure on them, eventually they will give in.