How to strict rp filter; manually

according to the docs on rp filter, "strict mode does not work with routing tables". that said, is there an alternate way i can do strict rp filtering, since we're using mark routing in places? maybe manually with firewall rules? could someone point me in the right direction.

all i really want is a firewall rule that prevents clients from behind vlan interfaces from spoofing their address and getting to where they're not supposed to be.