MS-SQL Server/TSQL Trigger: Update a field only when a specific value is set, otherwise set a different condition

tsql_update_field_when_conditional_value_is_set_trigger.sql

/*www.technical-programming.com, lo sauer 2013
Target: MS/Microsoft SQL Server 2005 or higher
description: Upon update, the rows's timestamp field is set to the current unix-timestamp, 
unless the timestamp is NULL or Empty. If the timestamp field is supplied in the update
statement, the supplied value is set as is.

The tstamp field is defined as:
    [__unixtimestamp]     INT             NULL
The primary key is defined as:
    [ID]                  INT             IDENTITY (1, 1) NOT NULL
*/

CREATE TRIGGER mytableAfterUpdate on mytable
FOR UPDATE AS 
IF UPDATE(__unixtimestamp)
	BEGIN
  	SET NOCOUNT ON -- Supress the trigger statements in the'affected rows' count 
  	UPDATE dbo.[mytable]
  	SET  dbo.[mytable].[__unixtimestamp] = Inserted.[__unixtimestamp] /* +1 */ 
  	FROM dbo.[mytable],Inserted, Deleted
  	WHERE dbo.[mytable].[ID] = Inserted.[ID] 
	END
ELSE 
	BEGIN 
  	SET NOCOUNT ON -- Supress the trigger statements in the'affected rows' count 
  	UPDATE dbo.[mytable]
  	SET dbo.[mytable].[__unixtimestamp] = (CASE WHEN Inserted.[__unixtimestamp] >'' THEN DATEDIFF(s, '19700101', GetDate())
  					   ELSE Inserted.[__unixtimestamp] END)
  	FROM dbo.[mytable],Inserted
  	WHERE dbo.[mytable].[ID] = Inserted.[ID] 
	END
	
/* Short alternative, for use in a productive environment */

CREATE TRIGGER kurseAfterUpdate on kurse
FOR UPDATE AS 
IF NOT UPDATE(__unixtimestamp)
	BEGIN 
  	SET NOCOUNT ON -- Supress the trigger statements in the'affected rows' count 
  	UPDATE dbo.[mytable]
  	SET dbo.[mytable].[__unixtimestamp] = (CASE WHEN Inserted.[__unixtimestamp] >'' THEN DATEDIFF(s, '19700101', GetDate())
  					   ELSE Inserted.[__unixtimestamp] END)
  	FROM dbo.[mytable],Inserted
  	WHERE dbo.[mytable].[ID] = Inserted.[ID] 
	END

so what do you do if multiple processes (triggers or other) are trying to update the same data ? deadlocked.,