I talked to a friend recently who read that article, and tryed urea on all of his coyote sets. He had nothing but problems with digging and working the edge of the sets. He reset all of this traps in new sets without using urea, and his problems stoped.
Its hard to beat plain dry dirt for wet weather trapping. Wet weather k-9 trapping is hard work, no way around that. One trick I do is after a rain, if freezing weather is not coming, is to just scatter a handful of dry dirt over a "washed out" set- this freshens up the set considerabily. Remember to blend in your dry dirt circle well with the rest of the set. Coyotes will shy from sets that are wet, with a dry circle over the trap. Two ways toi do this are 1)just use a little wet dirt in a very thin layer as a final covering and 2) cut up grass, etc to blend in the pattern......trappnman