Don't mark coins. It is utterly useless - no matter how much volume you do. All that marking dumps accomplishes is rubbing the hobby in the face of the banks and coin processors - that they are being manipulated and taken advantage of for this frivolous enterprise of ours.
Don't forget that, essentially, the only way that half dollar bags ever fill is if you or some other hunter dump into them. Either you are getting stuff that is stirred up by another hunter, or you are stirring stuff up for yourself (or for another hunter). The only input you should use to guide you where to dump is wherever they take your dumps for cash. The only input you should use to guide you where to source is wherever produces keepers at an acceptable rate.