Dog barking in apartment?

I had my dog a long time and hes really mean because we found him on the street with no collar. We saw alot of bruises on him.He was pretty bad and looked like he had an abusive owner and then we kept him he loves us but is really protective of us too because hes afraid someone gonna hurt him. So he also barks alot and I always run toward him and shh him up because we live in an apartment and I hate it when he barks because I dont wont people living downstairs to complain so anyways does anyone know what time is it ok for a dog to bark and does anyone know a good dog barking collar that works?