If the the cables do not intrude into your property then there is nothing you can do about this. Do they intrude?
For example: I cannot affix hanging baskets to the far side of my boundary wall (which I own) because they would be over my neighbour's land.
On a practical note, it is hard to buy mains-voltage garden lights nowadays. Low voltage cabling does not need special conduit unless it is vunerable to damage.



