The simple answer seems to be borax and white vinegar. One of our cats has been having bladder problems lately and relieved herself on Amelia's play mat and my shorts. In an act of desperation I tried soaking it in a mixture of Borax (20 mule team!) and white vinegar for a day (with water of course), then I put in the washing machine on the highest temperature setting.
Previously we had tried it on just the highest setting with only Borax...I think the soaking and white vinegar is the key here. At the least it doesn't seem to hurt.

So cat urine? Soak in a quarter cup of Borax and a quarter cup of White Vinegar overnight in a tub of water...then wash in hot/hot. You might just save some clothes...