Often times the phrase "hip extension" is thought of as a bad thing because you think of EARLY hip extension. That is the clue. Early hip extension is really bad for your impact, but proper hip extension adds a lot of power into your swing.
Hip extension is paired with hip flexion in the swings of great golfers. When you look at a swing from Rory McIlroy in slow motion you see how well he both flexes his hips - AKA "squatting" - and extends his hips in the swing.
In this video Dr. Tyler Standifird outlines how you pair hip extension with hip rotation to really drive proper motion of the pelvis and hips in the swing. You will be able to properly maintain posture through impact and contact and that is huge to get better ball striking.
Check out the drill at the end on the video and try it out the next time you practice at Alta View.