Yeah,
so I looked at the several pages on the internet, which contains this idiom "double down low"
and it seems it is term from the sport....like here:
(from the www page about basketball...)
....That depends on their guards. If they double down low, we need to get movement from our guards. (Mike Wilkinson and Tucker) are going to draw attention when we get the ball down low. We’ll rely on them to knock down shots.
So i think in my situation, "double down low" means this: .....secrecy is very important. So be doubly carefull.....
Otherwise, I really don't know how to translate it....:-(((
best regards
JCD