Enthrall Undead

Choose one undead servant that you control within range that was created by you (through a spell such as Animate Dead). This undead is now a thrall under your control until this spell is dispelled.

Undead that are your thralls are permanently under your control and do not need to have the spell that animated them (such as Animate Dead) re-casted on them at the end of the spells duration. 

These thralls operate the exact same way as the spell that animated them describes.

You can own a number of enthralled creatures equal to half your total caster level, rounded down. (minimum of 1).

When a thrall's magic is dispelled (through Dispel or similar effects such as an Anti-Magic Field), the thrall is no longer under the caster's control, and acts as the DM see's fit.