PPTP VPN + Client RB750GR3

Hello i fix one Vpn pptp with 2 RB750GR3 my server router they have 192.1468.12.xx/24 my client router they have 192.168.14.xx/24 i put one rule in the route table to watch the router network
but when the client disconnect and connected again i can see the router from the both sides. I find that in the route table the lost the name from the vpn how i can tell the router to watch them from the both sides ?