Hi Arukk,
You can implement a mechanism that would prevent concurrent updates by doing the following:
– use a custom action for form Initialization Action and store the list item Modified field in a session variable
– use a custom action and create a custom save that would perform the actions:
1. Validation of the record (get the actual Modified field value and compare with the value stored in the session). If they have the same value then is safe to update otherwise warn the user and cancel the save action
2. Save the value if the above step says so
Please check the documentation (section Custom Actions and qListForm Form Initialization Actions and Custom Actions).
If you have any questions please let me know.