I think I've found him on the 1881 census:
Llanganten, Brecon, Wales (Rg11 5455/90)
Frederick CAIRUS Head age 31 Born Witney, Oxfordshire Occ: gamekeeper
Emma CAIRUS wife 32 born Ledbury, Hereford
George F CAIRUS son 10 born Ross, Hereford
Emily A CAIRUS daughter 2 born Presteign, Radnorshire, Wales
Edward E CAIRUS son 11 mths born Penybont, Radnorshire, Wales.
I was hoping that I might be able to look up his birth/baptism as I have a few Oxon CDs from the FHS - but not Witney! Sorry!
Jill