If you want a big, active, loyal dog which would suite a warm climate and will help you if attacked, what about a Rhodesian Ridgeback [http://en.wikipedia.org/wiki/Rhodesian_Ridgeback]?
Being from South Africa they should be ok with a warm climate, and as long as you're not attacked by anything bigger and more savage than a Lion, they should be able to protect you too (they were bread to hunt Lions, keeping them at bay whilst the hunter moved in for the kill, so they've got courage & won't back down from danger).
As hunting dogs they're well suited to exercise, but apparently they're extremely strong, so if you're not also pretty strong yourself they may be a bit of a handful to retrain with a leash.