Presuming it is not in violation of your existing orders, you do not need to be physically present for your spouse to take care of the kids of whom you have custody. The extended absence could prove to be a problem if a physical or legal dispute occurred between your spouse and your ex while you were away.
At minimum, you should have a power-of-attorney drafted for all necessary health and welfare custodial purposes. A formal guardianship is probably unnecessary, since the children will remain in your actual, if long-distance, custody. If you think a dispute is likely, consider asking the family court to explicitly order the spouse to act in your absence in advance, which should shield against the chance that the ex might make a scene in your absence. For background, see:
http://willicklawgroup.com/child-custody-and-visitation/
http://willicklawgroup.com/guardianship/
You can file yourself through the Clark County Family Law Self-Help Center forms, or you can consult with, and file through, a family law specialist.
Answered on Jan 09th, 2015 at 5:18 PM