I don't do the love and logic thing....well actually I do 99% of the time, but I do include firm discipline within the loving logical standard instead of sticking to the positive parenting mold.
I have ALWAYS used warnings, because they cut out SO many needs for follow through. I ALWAYS explain things with no consequence the first time they do stuff. THEN the second time is a warning, re-iterating what they were already taught and giving them one more chance to act right, and the third time is a firm, consistent consequence EVERY TIME.
Now at ages 5, 3, and 2, the two year old being born with most difficult disposition, the warning suffices most of the time. I take them everywhere with me, their dad always travels. My five year old hasn't been disciplined AT ALL in years, she is extremely well behaved with her own firm compass, my 3 year old rarely is disciplined and he's also excellent, and my 2 year old, is doing really well catching on with more consistency and firmness than the other two needed.
Warnings are pointless if there is not an effective firm follow through consistently and immediately when setting boundaries. At five, he GETS IT and HAS all self control mechanisms firmly in place, you should not be battling him very often. He honestly shouldnt' need many warnings, since he knows all rules. A warning in advance about behavior before arriving at events and then IMMEDIATE follow through if he acts otherwise is what I would do. And I would firm up at home first, so you dont' end up leaving events immediately all the time and stuff because he pushes things in public still thinking expectations are new and negotiable. This book is very loving and positive, yet firmer and more consistent than love and logic, and could give you a good boost and help the hubs feel a bit less stressed: Back to Basics Discipline by Janet Campbell Matson..
Also, I don't undermine my husband when he's home- but that's not often :) I let him "seem to be in charge" so the kids feel secure in his leadership as well as mine. We get on the same page after the fact in private if our discipline opinions go awry. Dont' sweat it though, all is not lost. If you guys get on the same team, no one will remember this particular day!