Concerning Pepper and berar spray... Should be noted...
That these will not work on a truly determined dog.
Many of the clients whom I train with in regards to serious PP work will ask me to test their dog's will to stay in a fight or engage under the most dificult of situations imaginable.
To that end, we do not physically beat the dogs, but use as much "soft opposition as we can... ie, cardboard boxes, foam bats, split bamboo sticks, firemarms firing blanks, water oppostion...
I have use pepper/ capsaicin spray to test a dog's reactions several times. Mind you, as this point, these dogs were all mature, driven animals whom had several years of training behind them.
In the group of dogs that I used sprays on, I have not had one dog not engage the decoy, if the spray was fired before fighting contact was made, nor one dog break engagement, when the spray was used when the dog was already in hold... In fact, especially when used once a dog is already in holds with someone, I have found the spray usually increases their fight drive, and many of the dogs hit tend to counter against the spray (Get a deeper grip).
All to say that, while perhaps useful against the typical curs and other loose dogs one is likely to come across, it should not be viewed as a tool which will be useful against every dog.