Restrict traffic to particular gateway

[Azannah]

I'd like to restrict traffic from one of my subnets to a particular dynamic gateway (assigned via DHCP). To do this, I've set up a basic policy route:

All traffic (any protocol) entering interface X from subnet N (the only subnet on interface X) to anywhere routs through gateway GW.

When gateway GW is up, traffic routs as expected. However, when the GW goes down the traffic redirects to the default route. If GW goes down, I don't want any traffic from subnet N to get routed out of my network. How do I prevent traffic from sneaking out through the default route?

Thanks!

Matt

[Azannah]

Does the fact that the policy specified gateway has a dynamic address have anything to do with the traffic being redirected over default route when the gateway goes down? If the gateway specified by the policy route had a static address, would I be experiencing the same issue?