Checking the line was probablly what made me lose the fish. I had not yet checked the line that day though it was after less than ten casts that the fish broke off. I guess I should start checking the line more often.

If your cranking brush, you really need to be checking the knot every cast or two.  

Is the bait breaking at the knot or above it?

Above the knot.

if the line breaks and there is no wear on the line then your drag is too tight.

Someone posted a pic a while back of a bass they caught with a big crankbait still in the mouth.  Obviously that fish was still feeding, or at least trying to feed.  

You would be surprised at how well a fish can remove a bait from it's mouth give some time and slack.  Some will die but I think the vast majority will throw the bait.

All hooks at some point rust off anything in water.

Good lucks to you in catching the "BIG KAHUNA!"

But it may not be in time for the fish to be able to feed again. Given the quality and technology put into the coating on the hooks made these days to keep them from rusting, even the stomach acids wont rust them as quickly. One fish wont kill the whole population, although it will probably shake it free, but don't count on the rusting factor too much. Definitely check your line and knots after each fish, especially if  around cover, and the guides on the rod. All good advice to help prevent line breakage and losing lures (they can be expensive!), it'll also help land more fish.