Every platform that becomes popular eventually ends up being spammed.
My suggestion would be some kind of filter that keeps track of several metrics related to the domain name linked, ie how often the domain name is part of reports, how recently the domain name has been registered, etc and if the link seems untrustworthy, have the submission or comment filtered and require a manual approval by the community mod(s) before it shows up for everyone else.
And personally I'd auto-block any URL shorteners services, they don't serve a valid purpose here and can be used to hide the destination URL.