The best way to have no ich in the system is strict QT of all additions and if you want to be sure, remove all fish and treat them for ich while leaving the tank fallow 76 days.
I will be employing a modified version of the tank transfer method (TTM) for treatment. Quick summary, you basically move the fish every 72 hrs from one tank to the other, doing your best to minimize water transfer and not use any of the same equipment between the two tanks. Once transferred to the other tank, the original one is dried, cleaned with bleach or vinegar, and then reused for the next tank transfer. You do this every 72 hrs for 12 days and presto, no more ich. It interrupts their life cycle so once the parasite drops off the fish and starts to encyst, you would have removed your fish to the other tank by then and so there are never any hosts left to continue the life cycle process.
My modified version will include my giant UV sterilizer and instead of using new water each time, I will be passing all water through the UV to kill any ich and save time/trouble/money in the process.