They key to charming is to find what mobs make the best charm pets, and augmenting their DPS even more.
A few things to help:
1) Give your pets weapons. Once you charm them, they stop quadding unless you give them weapons so they can dual-wield.
2) Make sure your pet is hasted.
3) Make sure you are crippling the mobs you fight as well.
4) Block "Antidote" and "Frenetic Renewal" on your pet. Mercs have a nasty tendency to cure charmed pets with those. You may also wish to block "Complete Heal", if the merc is healing the pet too slowly.
5) Companion's Blessing AA works on your charm pet too, all activated pet AA's work on charm pets.
6) Tying an audio trigger to the charm break helps a lot.