Tips On Securting Sql Server

Hello I have 2 sql servers in my company and many remote sites. I am
trying to figure out the best way to keep them safe, since both have
access to the internet behind the firewall. I was planning to disbable
the default gateway on one or maybe disabling file sharing on both, i
was also thinking to block access to the the terminal server that is
running in admin mode, either through the firewall or the permissions
of the rdp protocol. I have a few admins that have account manager and
server operator permission as well as exchange admin. Any ideas in how
to restrict access to my servers? thanks.