Making NetVMs follow their AppVMs

[tetra...@danwin1210.me]

If I have a NetVM, called my-vpn-vm, that provides network to my-app-vm,
my-vpn-vm will automatically start when I launch an application from
my-app-vm.

However, when my-app-vm shuts down, my-vpn-vm will stay running.

Is there any way to:
a) automatically shut down a NetVM when there are no more VMs connected
to it?

or

b) automatically shut down a VM when a specific other VM is no longer
running?