Chum can be hard on fishing gear, especially the ones that are still fairly fresh fish. Twelve pound mainline, sounds strong enough, and you might even consider some of the braided lines as they are smaller diameter which allows you to put more line on. However, you should also use a swivel at the end of your line. That way you can tie on your leader material be it 8 or ten pound mono, before you attach it to your lure. That way if you have to break off a fish all you lose is the lure and the leader. Also be sure to check your knots and leader after every fish you catch. If there is a nick in the line, retie the leader and the lure and you are good to go again.