If you will apply several easy routines when making mission, it will help to make percentage of intercepts before the target close to minimum.
a) Never say the base your are up from and base you hit until the mission starts. Even then say it at mission channel only.
b) Always plan having second base/target in mind, if before the start of mission situation changed unfavourably, change start base and go for second target. Best to have those 2 tagers quite far away from each other, so if it is spying, guys who are up at other side will be bit frustrated looking for you where you are not.
c) If you go over dar make sure it is in a part of map where other side is not looking. OR hide your dar with long friendly dar in sector.
d) Always consider NOE.
e) There is spying, but not so many. Not every time you are out of luck, it is spying.
My last 30+ strat missions were successful, without a single case of what I think could be a spying. I saw spying before, but it is rather exceptions than rule. If you plan wisely, chances to be intercepted before you get alt/speed are not that big.