Rails - Apr 2006 - active record and tsearch2, works?

I have a search form; I grab the value and use it in a fulltext query:

:conditions => ["idxfti @@ ''" + search_string +
"''::tsquery and ...........]

Characters in search_string like "?", ":", bomb active
record.  I tried a
single tick and "\" to escape those, but active record still bombs
(same
queries via psql work).

Suggestions?
-Tate