Close but no cigar - the perfect Dengar is the following:
Dengar + Punishing One + Push The Limit + Recon Specialist + R4 Agromech + Engine upgrade
Once you're in combat range you'll take your double Focus and Push for the Target Lock. After your first red dice roll you'll use your Target Lock, then your Focus to get another Target Lock. When you get your second attack (you got your second attack, right?) you use your second Target Lock and second Focus to get a third Target Lock to start the chain again. Next round you can Focus + BR/Boost.