You could always use Global Fields for your related search. Each Global field is unique per user.
You can have a look at this video to understand a little bit more how you lock records
Sorry, I don't speak French. Filemaker will lock a record as soon as a user tries to modify it (unless the field is defined as global storage'). That is good database practice.
However I think your questions says that when a user performs a 'Find' in a portal it is locking the record for other users. That should not be the case - 'Find' mode itself (or performing a Find) does not lock any records.
Thanks for the tips !!!
With a Golbal Field it's work perfectly.
Simple & powerful.