We used the locked layer way as well. We have progress code included in Custom Fields so once a line or model reaches say code 4 then they have been issued for isometric. I know people can work around that but if you issue a Work note on it to designers explaining why they are being locked then generally people will abide by it. In the note you could also explain procedure for unlocking lines (go to admin to do it). We also did a change colour in Navisworks review model for any line that have reached code 4 progress code so you can see what has been issued to date in the model.