Choice of filehandle for flock utility

Question

The flock utility man page gives the following usage example:

(
    flock -s 200
    # ... commands executed under lock ...
) 200>/var/lock/mylockfile

Assuming 200 is the filehandle of the lockfile, is there a possibility that during some run it fails, because the same filehandle is already in use by other process? If so, are there any tricks to make sure locking with flock works reliably?