I would like to see a "proper" solution. Single IP monitoring is causing us no end of issues. Gateways being marked as down, but really the monitor IP has dissapeared, or ICMP is blocked but real world taffic tcp/udp is flowing perfectly.
My concept would include many IP's and have some weighted rules. Something like www.policyd-weight.org comes to mind.
This would allow a list of say 20 IP's to monitor and allow for x number to be down and some marked as higher "number value" than others, then only mark the gateway as down if the sum of these values is below y. Could even use the same IPs for many gateways and if one ip down on one gateway the IP can be checked against another gateway.
I have no development skills, but would be willing to test and give feedback.
–Paul