may he is having gas... most of the time when a dog's anal glands are expressed you can hardly avoid them smelling like anal glands for a few hours, so if that was not the smell you are smelling later (pretty unique odor, by the way), then it is probably gas or feces you smell... maybe having a bit of stomach upset... takes many days to weeks post anal gland expression for more to begin to leak out and smell again.

Allergies will often make a dog smell yeasty or greasy if they are developing secondary skin infections (more often than not NOT due to diet, though).

Yeah, skin infection was the first thing coming to my mind too. Some breeds get it in that crease just above the tail. And laughin about the breaking wind remark. It surely could be. My daughter's ridgeback used to slip out some silent but deadly ones, and usually when he was nervous.

I suppose it could be gas but it sure doesn't smell like any gas he's had before!! My huband made the comment today that our dog smells like he has an infection.
Would I be able to see a skin infection? I don't notice anything out of the ordinary but maybe I need to look closer.

I hear you about infections having a particular aroma. Maybe you should sit down with him and give him a really good brushing and inspect the skin under his coat as you do it to check for hidden wounds and any signs of skin flaking or inflammation.

Since the smell comes and goes, I would question it being an external infection- but that doesn't mean you shouldn't inspect his skin as was suggested.

I had a black lab mix who eventually had her glands out due to chronic infection. She did not scoot or lick because they didn't get impacted. Hers leaked and she left funny bad smelling spots around the house, sometimes we would find a spot of liquid, but most often we would not find any evidence except a strange smell lingering in one place- and not always where the dog was at the time the smell was discovered. In fact, early on we had trouble pinpointing the smell to the point that DH ended up taking apart a dishwasher thinking the smell was coming from that (the dog spent a lot of time sleeping in the kitchen). There is a peculiar distinctive smell about anal glands. Strong enough to invoke the gag reflex.

Our dog's anal glands would often overact when she was excited or something startled her. Accidentally drop a book on the floor and wake her and the smell would follow almost immediately. Does your dog make the smell more when he is excited about something? I'm wondering if it's possible that his scent glands are being activated by stimuli of some kind? I'm not sure anal glands work that way (my understanding is that they release their fluid during a bowel movement), but I'm pretty sure that our dog's could function somewhat without pooping and it takes almost no fluid to give a lot of smell. But again, our dog's could have been like that due to chronic low grade infections.

That said, my current cat has weird gas from time to time. He sometimes smells a little like anal glands when he is gassy- but not strong enough to make me gag like our earlier anal gland issues. We give him probiotics, that helps a bit. One thing I did not know about anal gland health back in the early 90's when we had our young dog, is that canned pumpkin in the diet can sometimes help (bulks up poop and helps clear them) and that lots of exercise can also help. Who knows if it would actually help, but it probably wouldn't hurt to try.