I have seen a telephone/power pole completely block a single C-band satellite due to perfect alignment of that satellite with the center of the pole. Also remember some issues when working under power lines that are line-of-sight with terrestrial interference. Interference can be transferred with hard-to-predict bounce effect from original source and possibly take out your reception, especially if that bounce happens to land in the vicinity of your feedhorn or LNBF. Not common but not impossible.