When urine comes out fresh its an acid, so use a higher PH product. If its been in the carpet for some time it is going to change its PH to alkaline so you are going to need to use an acid to break down the urine salts prior or you might not remove the odor that is within the salt.
Gravity takes the urine all the way to the subfloor, which is most usually a wood subfloor (at least here) so you have to recreate to accident and get your product down to the subfloor. The pad is like a sponge and will absorb a lot of urine, so light it up and pour it on.
But before all of this you gotta pre qualify the job, like with any.
I like to use multiphase from
Jon Don, it has taken care of all my odor issues... even the ones related to carpet cleaning.