We keep everything behind a single strand of electric, but two rules
1. they MUST be trained first.
2. if they do get out, they must still be within your property, and not able to wander to somehwere where they can do harm - they don't immediately rush to the next boundary to get free, they investigate the new area they have found, in our case fields that are sheep fenced, but certainly not pig proof.
We've only had 3 exceptions in 16 years - a Tamworth who stepped over every day at meal times to greet us, a GOS (but only one of many) who just walked through yelling as she went and was always out, and a middlewhite who came form a farm where she was behind a 3 ft wall with a strand of electric on the top - that should have told us something !
We now have LB, GOS, SB, MW, Berkshire, Landrace, mangalitza, OSB all behind a single strand.