There is this stuff my fiance uses for when we had the puppy and he would poop on the carpet, I also used it when he pooped on my leather couch, it's called Odoban. It didn't say if it was safe to use on a couch, but I used it and then wiped it, and then used a leather lotion behind it. The stuff is amazing...you can use it to get rid of any smell....and you can get it at Walmart in a spray bottle or a gallon container. I suggest buying a spray bottle and getting the gallon, cause you're going to love this stuff. It deoderizes, disinfects and cleans.
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There are proteins in the urine and feces that have bacteria which leather absorbs, you need something that will absorb into the leather, neutralize those proteins and not damage the leather. I will not go into detail how I know this will not only work on the couch to clean, condition and deodorize it, but It has been used to remove far worse smells in enclosed areas on leather that does absorb odors and hold them due to bacteria.
Gold Class Rich Leather Aloe Cleaner http://www.meguiars.com/estore/product_detailpage.cfm?product=Gold-Class-Rich-Leather-Aloe-Cleaner&sku=G-110 and follow it up with Gold Class Rich Leather Aloe Conditioner http://www.meguiars.com/estore/product_detailpage.cfm?product=Gold-Class-Rich-Leather-Aloe-Conditioner&sku=G-111
You might also find a car detailing shop that will sell you some of this locally, it is one of the better products that is used by them remove pet orders on furniture and other smells from body fluids on leather car seats
If any fluids absorb so far in that it has got into the fiber stuffing of the sofa, you may have to have the sofa opened and those fibers replaced or cleaned also. Before I did that, I would also try a spotter enzyme like Liquid Alive Enzyme Digestant to try on the surface area where the accident happened and hope that it sinks in as far and neutralizes the proteins and bacteria there