Need to secure my Management plane Publicly from outside?

I have a router which is connected serially at the outside WAN interface. I have IP SLA configured in it to my Solar-winds monitoring server IP whose traffic traverses via the same IPSEC tunneled secured intranet path. But, the problem is that inspte of SSH being configured correctly (router asks for  password when SSHing to LAN IP), I still am unable to secure my management plane publicly through my WAN IP (someone removes the IP SLA Monitoring command again & again from the router), since it doesn't asks for login enable password credentials on SSHing to WAN IP from outside and directly enters into *my_router_hostname*# (hash) mode.