Scratch that, add this to HandleTarget.cs and Sentry will forever be spammed:
if (!Player.IsIncapacitated
&& CombatBase.CanCast(SNOPower.DemonHunter_Sentry, CombatBase.CanCastFlags.NoTimer)
&& TargetUtil.AnyMobsInRange(75,1,false)
&& Player.PrimaryResource >= 30)
{...