How Do I keep Our Ferrel Cat Out Of My Garden??

We have two cats both sisters and both ferrel. One we keep inside because she let us pet and hold her but the other is very leary and will not allow anyone to pick her up and definetly will not stay in the house . We tried but she won't have any of it. Both cats have been spayed by someone and then turned loose on us. Of course I feed the outside cat as well and had the inside cat taken to the vet for its shots but the outside cat seems to be doing a lot of damage to my container plants and I just don't know how to prevent this problem? HAAAALLLLPPPPP!!!!!!