They'll need training to it, and they will continually test it...
Before I get more detailed, please note that electric sheep netting cannot be used with horned sheep, so for Sh1tlands, only lambless ewes (or ewes with only ewe lambs) and of course any occasional polled males.
Whether using tape, rope or wire electric fencing, test
every section (ie., after every join and gate) of
every strand, when you put it up and at least once a week. When I say test, you need to know it delivers a measurable shock, so the little "beeps in the presence of a current" testers are
useless. Either get a meter that gives you a measurement, or become adept at "reading" the blade of grass test. (I use a similar length and width blade of grass, and know that I need to feel more than a tingle before I have slid it to within 2" of the fencing material.) Until we tried containing my little Sh1tland x sheep, we had no idea just how poor our tape joins were, and the extent to which - and speed with which - tape and rope deteriorates. Nor how quickly the shock at the furthest point from the battery reduces as soon as the battery starts to lose charge.
For adult Sh1tlands, have the lowest strand no higher than top-of-front-legs height, and the next no more than 8" above that. A third strand above that with insufficient gap to encourage the brave or fearless to try a leap, and the top strand high enough to discourage an attempt at hurdling over.
Wool is a phenomenal insulator, so the fence needs to be set up so as to ensure that they have to press an unwoolled part, or really squeeze through so that the wire (wire is much more effective than tape or rope, but less visible, so maybe use some of each while they're being trained to it) presses the wool down sufficiently to reach the skin, or very nearly. If they can limbo under the bottom strand without their backs lifting it up, they won't get much of a shock at all, except maybe when very recently shorn.
If they can lepp through between strands or over the top, they will not get shocked even if they touch it, as there is no ground contact

Lambs make it all much much harder. They can get through tiny, weeny gaps, they are well-covered in a highly proficient insulator, and they have extremely small points of contact with the ground. Once her lamb is through, the ewe may well be prepared to withstand a shock to get to her baby - and after that, she knows it hurt, but didn't kill her.