Well, you made the mistake of feeding him...even once is too much. I would try the humane trap and relocate him if possible. I would not take a chance of losing my cat by turing it loose though! If all else fails...an air gun? blast him with a water hose when you see him? borrow a neighbor's dog?. Good luck, I know it is sooo frustrating after all that hard work in your yard!
...and when you figure out how to get rid of him....please tell me how to get rid of the 3 skunks that are living under my house! :shock: