The message
from "Steve - www.ukspeedtraps.co.uk" contains these words:

We laid a new law about 2 months ago and we have had a few patches of dead
grass. The patches have a very strong ammonia smell, so strong that
when you
put your nose near the grass it almost blows your head off..

Today I have found another area on its way out so I have replaced that the
same way. Now I am very sure she did not use this area so I am looking for
other answers.

Dog and human pee smells of ammonia. Possibly a dog attracted to your
bitch but in that situation most dogs only mark the spot briefly so it
would be unlikely to cause such a strong smell.. More likely a person,
especially if you live on a tourist route, or near a pub or sports
stadium.

Foxes can climb or jump anything a cat could, so could easily jump a
6ft fence, but their smell is very different from ammonia:, it's a
pungent musky pong nothing like urine.

Janet.