The ‘Record’ form of redirect_to uses the second argument only for the response status. You’ll have to use another form of redirect_to, like the ‘String’ form. e.g.:
redirect_to thing_path(@thing, :foo => params[:foo])
which will work for nested params[:foo] params like you mentioned. Or, as Drew commented below, you can use polymorphic_url (or _path):
redirect_to polymorphic_path(@thing, :foo => params[:foo])