There's not really any reason that you would ever have this power turned off. Rather than having a maxed out dodge/parry and then this power as well, you would build so that they're maxed out including this power.
If you do want to be able to turn the power off - or you're worried about being defenseless if your power is nullified - then you can reduce the ranks of dodge/parry that are coming from it and put them just straight into your defenses. You're not saving or spending any additional points, but you could have (for example) a base stat of 7 in both your dodge and parry, and then this power increases both of them by 3 ranks and adds the Impervious extra. This would be 3 ranks or Enhanced Parry and 3 ranks of Enhanced Dodge (for 6 points) and then Enhanced Extra: Impervious on both your dodge and parry (for 20 points) rather than the first bullet point. The power's cost is reduced by 14 (to a total of 41 points) and you spend an additional 14 points directly into your Defenses.