There would be the normal issues of the fact that you are not allowed to possibly injure those who are trying to steal from you. I disagree with this, if they want to cut the cables live, then hopefully Darwinian selection will kick in, but, I don't like the idea of locking the isolators on, as this would be too deliberate an act, and in the event of one of your people needing to isolate in an emergency you cannot. You, "could" re-locate the isolators, and work on a PTW & LOTO system with them, where by whilst the isolation is not immediately local to the units, it could be local enough to comply and as long as it is in control of the person working on it, which if the person has undertaken LOTO it would be.

Duty of care ..... including to those who may not legally, but foreseeably be present at site. Lots of local news stories can be found on the web regarding people injured / killed cutting cables on transformers / street lights to steal the copper seem to indicate a mentality where seeing the power switched on would not necessarily be any form of deterrent. And if they have "come equipped" pretty sure they would soon be through any lock out system ... as our old Security guard often quoted "locked doors only keep out honest men"