Question about Guarded by the Light

In 3.1:

... and gives a 100% chance to refresh the duration of your Divine Plea when you hit an enemy...

So this means to me that I can cast Divine Plea and keep it going basically forever as long as I'm hitting a mob.

Am I correct in my assumption?

Yes. So long as you're meleeing, the buff will refresh.

Your assumption is correct, altho a use of Search would have found this quicker probably.

It's supposed to be there to fix our mana issues while protdpsing or temporary offtanking without taking damage.

Strangely enough, when I tried it on the PTR:

ShoR will not refresh it, while HotR does. IIRC, a straight up Judgement also counts.

Judgement and HotR are melee attacks (judgement has anti dodge/parry properties) while ShoR is a ranged attack.