I guess I don't know what you mean by "not secure"...
A PBL file on a LAN drive can be copied onto a thumb drive just as easily as one on a local drive, so you can't be concerned about file security... If you mean "not backed up", you always have the latest and greatest checked-in code in the SCC repository. And there's nothing stopping you from placing PBLs on the LAN, just make sure everyone has their own workspace copies. Don't all work from the same shared single copy of the PBLs.