Well, to the trout, there is no doubt you are foe. So don't let the little fellows on sentry duty raise the alarm when you crawl into position to cast to the nice BIG fellow you have been watching from downstream.
The photograph below (click on it for a bigger picture) shows you the situation, but it is difficult to see the little trout on sentry duty in the glide to the left of the foreground.
Sentry above here ^
Your strategy in a pool like this is to catch the sentry first. Return him gently, but downstream of you and aimed towards a weedbed. So, instead of tearing off upriver, he makes for cover under the weeds. Then you can make that cast to the big fellow...
Of course they are not really on sentry duty. They just want the trout in front to not be there so they can move into the better place. Eventually, if all goes well for the sentry, it moves up through all the better places until, one day, he or she is the boss fish in the boss place - with sentries of his or her own to warn of danger.