I recommend not to Freeze Dharok without prayer unless you can do it with out it ever hoping to reach you. The best practice targets are Torag and Guthan. Another hint: Mage Karil, at your melee stats, you will waste too much prayer on him, so mage him. Dont worry, his mage defence, despite having the best mage defence armor, is still horrible. Last thing: Never EVER let your prayer down below 15 if you are using prayer unless you are absolutely sure you dont need it. Against Dharok, you wont know what would happen.