WordNet (r) 3.0 (2006):

fence in
    v 1: enclose with a fence; "we fenced in our yard" [syn:
         fence, fence in]
    2: surround with a wall in order to fortify [syn: wall,
       palisade, fence, fence in, surround]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "fence in":
   beleaguer, beset, besiege, blockade, bottle up, bound, box in,
   box up, cage, chamber, check, cloister, close in, compass, confine,
   constrain, contain, coop, coop in, coop up, cordon, cordon off,
   cork up, corral, crib, detain, encage, encircle, enclose,
   encompass, enshrine, hedge in, hem in, hold, hold in custody,
   hold in restraint, house in, immure, impound, imprison,
   incarcerate, include, inhibit, jail, keep in, keep in custody,
   keep in detention, kennel, leaguer, mew, mew up, pen, pen in,
   pen up, pocket, pound, quarantine, rail in, restrain, restrict,
   seal up, shackle, shrine, shut in, shut up, stable, surround,
   wall in, wrap, yard, yard up