Thanks Randy,
I have also found a referance to the 3rd and 15th Tex Cav as guards,maybe after Anderson's/Border's Regmt Tex Cav.
A portion of the 15th Tex Cav not captured at Arkansas Post returned to Texas and did guard duty at Camp Ford.
Ref:
1."A Yankee Prisioner in Texas" Pvt William Ryan 160th NY Vol Inf
2.Regmt history of 15th Tex Cav
Mike