Some interesting subjects this evening! Urea/uric acid ( found in urine) is found in many skin products including e45 creams and lotions for its beneficial properties. Have a look at the labels of some of these products.

I think all urine puts off foxes and cats ( didn't know about slugs- I just know they like beer and thought they were hemaphrodite anyway ) but the male hormones ie testosterone is more repulsive as generally its male animals who spray to mark their territory indicating to others that this is their patch hence its more effective.