Maybe its just a bit old school, but I make sure my focus target is my Beacon target. Using X-Perl, I have made my buffs larger than everyone elses, and can easily see the time remaining for Beacon.
If, for some weird reason, my sacred shield target is different than my beacon, I have beacon on focus and regular target as my sac shield. Of course this means I have to alternate between zapping a mob to keep the haste up and going back to my sac shield target, but it works.