I've looked at this and a few other ActiveRecord vulnerabilities that look arcane at first sight, but the simplest solution that covers all of them is to first

I've looked at this and a few other ActiveRecord vulnerabilities that look arcane at first sight, but the simplest solution that covers all of them is to first check whether params[:something] is nil and refuse to do any DB stuff if it is, and second to explicitly convert all of your params[:something] input to the types of data you were expecting, using to_i, to_s or to_f. Additionally, if using where clauses, strip the input of all apostrophes or double quotes. I don't think there would be anything left to exploit if everybody were to adopt this semi-paranoid approach to protecting your code from bad input.