A question about mind shield

[betatester]

I wonder if the base is knew because  it was already attacked is building a mind shield still useful ?
If a base with a mind shield is attacked is it worth it to keep it (because they know where it is now)?

[Stone Lake]

Mind shield halves chance to discover your base every tick (IIRC 30 minutes?) that UFO flies over your base. Nothing more, nothing less. Compounding results from more - 1/3 chance at 2 shields, etc.
A base that was once attacked (as in - ground battle defended) actually "disappears" from alien radar and needs to be discovered again to be attacked.