There's no direct flag to disable migration for specific containers.
However, there is a way to force the migration failure by adding a fake template to the configuration file of the container:
[root@vz ~]# grep nomigrate /vz/private/101/ve.conf TEMPLATES=".nomigrate"
If TEMPLATES line already exists - append ".nomigrate" or any other fake name to the list.
Note: Not only migration process is affected by this solution, but also a restoration of a backup will fail. If it's needed to restore the container successfully, run
vzarestore command with