create trigger <trigger name> ON <table>
for update  
as  
begin
    -- exit trigger if update is on LastUpdate field
    if update(LastUpdate)
            return

    -- get key field to use for filter
    declare @lckey char(20)  
    select @lckey = <key field> from inserted  
    update custFL set LastUpdate = GetDate() where <key field> = @lckey
end