Setting DNS configuration network wide will prevent most users from trying to bypass the system. Most routers and firewalls allow you to force all DNS traffic over port 53 on the router/firewall. In additional you can create firewall rules that allow only ScoutDNS resolvers while blocking all others.
While exact commands may vary based on device you essentially want to create rules like this:
ALLOW TCP/UDP IN/OUT to xxx.xxx.xxx.xxx on Port 53
BLOCK TCP/UDP IN/OUT all IP addresses on Port 53
On some firewalls you may have to create a separate rule for each protocol instead of one for both.
Due to the huge number of devices on the market, ScoutDNS is unable to provide support for your specific firewall/router. Please consult your manufacturer if you require assistance.