Much of the weapon retention tactics taught in police academies are based on a marshal arts system developed by Alvin Lindell. They might be available on youtube.
I'm not a fan of open carry as I feel that if someone targets you to get the gun, he'll probably succeed. Likewise, if you're targeted for a robbery, the presence of your gun could prompt a pre-emptive strike and you'll be shot before you know you're in a gun battle.
I also find it difficult to have respect for someone who needs to open carry during the course of routine social interaction.
Int'l Assoc. of Law Enforcement Firearms Instructors