A general Power of Attorney will do, but he needs to make sure the POA contains the words specifically to negotiate joint Income tax refund check. The POA can also be limited to this one item.
However, when I was in the Military, I required all of my soldiers on deployment who had families to execute general POA's for their spouses who were remaining at home. We referrred to this as family readiness.
For your husband's deployment as it were to Israel, I would say he needs not only a general POA, but also a living will, AND a regular will.
In many cases, the company a person works for has their own notary which employees can use. However, any notary would work.
You need to also know, that a POA is not absolute. There is nothing in law that absolutely requires the person at the bank or any other person to accept the POA.
You still may not be able to access the funds for 10 to 15 days after the check is deposited.
In your situation, I would make sure the indorsement carred the for deposit only statement that I indicated earlier, and MAIL in the check. At the same time, I would obtain your husband's POA. It will most likely take a week or two to get the POA anyway. By then the check would have cleared. If it doesn't, and they return the check, then you will have the POA with which to try again in person.