secure connection between sxt en rb

Hey
I setup a ptp connection to a remote location with sxt antenna,s. I use an rb951 as local router to provide wifi in this remote location. The RB get,s an ip from the main router in the headquarters. It was not possible to mount the RB in a secure location. So, its possible to pull out the connection between the sxt and the rb and use a swith to interrupt the connection and use the network unauthorized. Is it possible to secure the connection between the sxt and the RB and only allow traffic between those to devices?
Regards,