Fishy smell leakage.

Oh, please,  that wasn't graphic at all!  []

In fact, you gave a very good description. 

Very close to the back end opening are anal sacs, frequently call anal glands.  They secrete a dog's very own particular scent.  Which is why other dogs are always sniffing back there - it's there version of a handshake.  "oh, that's who you are....I've smelled that scent before. glad to finally meet you". 

They "should" get emptied when they go poop.  But in some dogs, this doens't happen at times.  Sometimes adding in a little bit of fiber will help.  Sometimes it doesn't.  You might want to try adding just a bit of grated raw veggies into his food.  Or maybe even cooked.  There are other things to try.  Whatever you do, I wouldn't add too much b/c he is a small dog, especially at first.  His body would need to get accoustomed to the bit of extra fiber.   And, it might not help at all.

Either way, the first thing is a trip to the vet to let them show you how to "express" them yourselves.  Basically, you put on rubber gloves, get some "personal" lubricant (ky gel), and gently reach just inside - barely inside- at the 4 and 7 o'clock positions. (edited to restate it is 4 and 8 o'clock position - in that general vacinity).  You reach to the back of the sac and gently squeeze foward, making sure not to block the opening in the front of the gland so the liquid can come out the normal exit.     It is truely best to let a professional "walk" you thru it the first time.  Don't just let them do it, but have them show you how to do it.  Otherwise, you'll have to go back each time.

It may never happen again, and it may be a somewhat regular occurence.  They can become "blocked", so you do have to "express" them.  You should not just ignore it and hope it goes away.  It won't and they could become "blocked".  No emergency to go to the vet, but do make an appt. and learn this wonderful aspect of dog ownership. [&:]

chasza explained it well, but I just wanted to add that he could be expressing because of fear, also. Has he been licking or chewing back there? Dragging his bum? A vet check isn't a bad idea, just keep in mind it could be fear expression also. I have one who does that. []

If the kid was bothering him, and he was afraid, he might have expressed the anal sacs out of fear.  Nasty stink, isn't it? []
Just be sure that he isn't impacted, and keep little buggers from bugging the dog and you should be ok.  Petastic will probably get the smell out nicely.

I just posted in the health section that Sassy used to have this problem too.  I'd never had a dog with anal gland issues and thought it was urine leaking but couldn't figure out why the smell was so awful [:@].  When we changed her food, the problem went away - thank goodness!!!

I always called it the Rotten Mushroom smell....  Whenever Nikki leaks a bit we say she's "mushrooming" again []

Yeah, I think it smells like funky mushrooms too. We're not as delicate about it as you are, Nikki, we just say, "Ew, it smells like dog butt in here." Conrad is prone to random expression. We'll just be sitting around all nice and happy and all of a sudden Conrad gets this "who farted?" look on his face and then starts licking his behind, and then the rest of us get the whiff. It usually gets Conrad an express ticket to the great outdoors. We've tried altering his food, giving him more fiber, less fiber, this that and the other, and it still happens.

Just another magical moment in the life of a dog owner.

One more thing to add, some groomers will express the anal glands too, and/or show you how.

ORIGINAL: houndlove

Yeah, I think it smells like funky mushrooms too. We're not as delicate about it as you are, Nikki, we just say, "Ew, it smells like dog butt in here." Conrad is prone to random expression. We'll just be sitting around all nice and happy and all of a sudden Conrad gets this "who farted?" look on his face and then starts licking his behind, and then the rest of us get the whiff. It usually gets Conrad an express ticket to the great outdoors. We've tried altering his food, giving him more fiber, less fiber, this that and the other, and it still happens.

Just another magical moment in the life of a dog owner.

Funny how everyone has their own special names... because it has such a bad funky smell, we say, "Ugh, Rupert butt-funked again."
We've also switched his food a bunch of times, added pumpkin, and he still randomly "leaks."

ORIGINAL: houndlove

It usually gets Conrad an express ticket to the great outdoors.

Well you're lucky he does it when you can just send him outside...Nikki's prone to the frequent expression as well, but it's usually when we're all crammed into the car with her.  And of course, guess who gets to sit right next to the dogs... [&:]