Thought about using Stainless steel wire rope? and then one of those screw things you screw into the ground?? and when lead the wire up into a tree (not too tight.. i'm not saying hang her) so its harder for him to cheew?
>pic related>link for a britbong>https://www.ebay.co.uk/itm/Stainless-Steel-Wire-Rope-cable-2mm-3mm-5mm-thickness-PVC-coated-FREE-DELIVERY/291905590861?var=590901802262&hash=item43f6edd64d:m:m1v4hxk62-0W3noqoDb3p2w