I'm by no means an expert on ANYTHING. - that's my disclaimer -
I'd say it probably depends on your goals. The typical bodybuilder approach to dropping fat is empty stomach cardio with maybe some stims and BCAA's during the trip. Hopefully that will strip fat off of you and won't impede your strength. Whenever I start doing any cardio or dieting, regardless of what I'm doing for caloric intake, it seems like I get weaker.
If you're trying to keep your current weight or move up...definitely eat before, during etc...if you MUST walk your dog.