When a rear naked choke is sunk in deep and properly, are there any effective techniques for escaping?

You can escape the RNC even if its locked in. The percentage of success goes way down but you can get out. With the RNC its the second hand behind the head that puts the pressure and actually makes the choke possible in most cases. If someone locks the second hand just keep reaching back and pulling it back out. Once you've done that you need to keep control of that arm so they don't lock it again. Next you can start working to get the arm around your neck away and pop the hooks out. Also if the person crosses their feet between your legs you can footlock them. If the person has a figure four bodylock you can do a few things. You can roll to one side so the persons feet are touching the ground. From there you can do a foot lock. Look on youtube under "body triangle". You can also bridge up so you push your body perpendicular to theirs and turn around. In a street fight I guess you can go for the eyes or something if the person doesn't know how to properly lock a RNC. I suppose you could also try breaking fingers but usually thats hard if the person knows how to lock a RNC.If you are both standing you can squat down a little to get your hips under thiers and then go for the throw. If the have hooks in and your standing you'll need to escape a hook to do the throw. If you get one locked on you, you better act fast because your out in a couple seconds. There is always a right and wrong thing to do but the right thing doesn't guarantee success. Theres hundredsof little moves like wristlocks and armbars that you can get when someone is one your back also but thats only if they're very inexperienced. Good Luck