well, he's the only one who can keep a stable bubble.
Those runes only halp suppot it. It's a 1 direction repellant. Example: Your sight range. All you can see, is repelled. But anything outside the "sight" of the rune's front, will wash in. That means, the group would have to hold a rune to the left, right, front, back, and above, to keep a bubble. BUT! You'd have to stay in a close group, or the water will cave in where the radius' do not touch... :/ THUS, you need a mage, so you can simply provide support. And, you have to channel the ernergy, and not just tie it to a person's head, and torso... :/