Angela, it looks like there is a garden in front of the fence, right?
And it's a rental, so WHY can't you simply pour a small slab of concrete in the hole and along under the fence. Looks like the garden/bark etc would cover it up anyway.
Have you told the real estate you rent through about the state of the fence and what is happening. Hell, I would have and asked that the landlord either a) Fix it pronto. Or B) I'll concrete it.
Hope Batty is okay.
Police can't help, nothing to do with them actually. Council can't help too much in this regard either TBH.
Stupid fools of neighbours. Hand grenade?