Greetings, I have a bull breed pup.   

I intend to buy a clicker tomorrow after reading some of the other posting.  Bless, no longer responds to her recall word.  I take her classes but wondered whether you have any points that could assist. 

Many thanks in anticipation :o)

This website has a lot of good articles that might be of use:
http://www.clickersolutions.com/articles/index.htm

http://www.dog-secrets.co.uk/behaviour--training/why-wont-my-dog-come-back.html