The back glass is not something to avoid. It is part of the court and often gives you more time to defend a deep ball. Rushing to hit every ball before it reaches the glass can force you into awkward contact points.
The first skill is giving yourself enough room so the rebound can happen in front of you rather than directly into your body.
What to do
When a deep ball is travelling through you toward the back wall, decide whether taking it after the glass will leave you in a better position. If it will, let the ball travel, read the rebound and play from balance.
This does not mean every deep ball must be left. The point is to recognise the glass as an option instead of automatically snatching at the ball early.
Why it works
Good glass defence looks calm because the player has created space and time. The ball reaches the wall, rebounds into a playable area and the defender can rebuild the rally.
For many club players, simply stepping away from the back wall and trusting the rebound makes defence much easier.