parental controls with personal modem: Arris SB8200 and Google mesh wifi

Google wifi parental controls works well for obvious filth, but has no ability to add custom URLs ore block NSFW content from sites that sometimes have decent stuff like twitter, reddit, etc.

I cannot use xFi because I don't have comcast gateway.

Is my best bet OpenDNS then? Are there directions anywhere?

thanks for your help.

c