Hi,

I might suggest trying an angle change for the direction your hands
point during chi sao. I notice both of you frequently have your hands
pointed straight up.
We have found that keeping the hands pointed
directly at the partner's center nearly alwsys helps to maintain the
forward energy focus and takes less time to slip into openings.
We will rarely let the forarms come to a 12 o' clock position,we try
to keep the forearms aiming forward at all times if possible.Some of
us even carry it to an extreme and always keep both the fok sao and
tan sao fingers themselves always pointing forward during chi sao.
On the other hand, I have noticed that when my chi sao partner does
allow his hands to raise too high,or points his hand to the side, it
triggers my reaction to further control his forearm with more
extension using an upward facing palm or similar.
Sometime, just for fun, try keeping your hands and arms pointing
forward and no higher than 11 o'clock,you might enjoy the results.
Cheers