
Yes a crate is a cage for dogs and you get usually get them from the pet store. Go in and ask, if they dont have any they will know of other places that do. I am a big fan of crates also but only for nighttimes or if we are going out for a short time.
I'm not a staff owner but it sounds to me like typical signs of boredom/frustration. Does he get a nice walk OFF of the lead+harness everyday? With nice fields to roam.
Even small dogs like staff need to get rid of energy.
Also, he may be a very intelligent dog and needs something else to get his 'teeth' into :p
Give him lots of new things to work out. Buy a 'kong' from the pet store and stuff it full of yummy things. It takes them ages to get it all out, and gives them something to do.
Also, I like to hide their toys around the house and play games where they have to sniff them out. They love it.
Good luck