I don't really have any great advice except to say that it's a constant work in progress so don't let the off days ruin how far you've come. I would continue letting him off in that field, but not close to where he escapes and not letting him off to his own devices - that could be where he gets some ball throws, where you practice some outdoor sit/stays or touches, something engaging so that he doesn't have time to think about taking off. Quinn will be 5 at the end of this year, so this is the 4th summer that I've dreaded water/balls/beach - this is the first year that she hasn't been taking off to get someone else to throw her ball, or just running rampage in general. It feels like a miracle, but it's not really....it's been 4 years of careful selection of when she can go off leash, the perfect timing on recall and practice, practice, practice. I feel like I know her better as the years pass, so I can really predict what she will do before she does it. You will get there!