It means to keep somebody/something at a distance.
e.g.
Seal had a hard time fending off fans as he trotted out of his hotel.
or
26 Dec 2010 "... Further north, an Afghan village fended off a Taliban advance. ... "
http://www.csmonitor.com/World/Asia-South-Central/2010/1226/How-one-Afghan-village-fended-off-a-Taliban-advance
