Having him altered may help, but if he was not really a pet and his behaviors are set, it may not. Have you contacted Cats International? They have some good advice on this sort of situation.

I have a cat right now who was fixed and declawed and then dumped out in the country most likely because he is a territory "marker." He will have a safe home with me and if (the Powers that Be Forbid) I end up having to move, will come with me because I don't think he will ever "get it." Better a safe home than the chance of being dumped over a natural behavior pattern.

Your run looks like a nice place to spend time and he could be in with you to supervise for play and cuddle time... I may be wrong, but I believe I've read that Bengels are sometimes problem children in this area anyway. If you can keep him, I hope you will.