buy some greens from Billy, the more expensive the longer the chocobo stays, as soon as battle starts and a chocobo is involved feed the greens to the chocobo, also try to kill off any monsters as quickly as possible, the longer the fight lasts the greater the chance of the Chocobo running away, don't use area effect skills/magics as hitting the chocobo even once loses it for you, personaly i'm usualy Lvl.20 by the time i make it to the Ranch so killing the monsters off fast isn't a problem, it's mostly speed and some luck that are the main factors with some good greens thrown into the mix... and if all else fails read "The Chocobo Manifesto" on GameFAQs...