Unfortunately it's not hard to manipulate this one. AR generates a couple queries when you do a single invocation - the first is a meta data query to get info about the table you're talking to. The second (or third, etc) are the actual hard queries.

It's the first query, the metadata one, that applies the passed arguments in a raw form directly to the query. The exploit takes place inside of a 'show' operation. It's totally unprotected and lets you run pretty much any select you're interested in.

It also goes beyond prepared statements - the metadata query in question is totally separate from the one specified by any parameterized query you'd pass using something like ('id = ?', params[:id]). So essentially, as a developer, you can't do anything better. This is kind of on the framework side alone :/