I am not really know what do you want, but I think you need raising one action when number of records greater than 2.
It will change when you insert record, that mean you must create a trigger for insert action as follows:
CREATE TRIGGER <trigger_name>
ON <table_name>
FOR INSERT
AS
BEGIN
declare @count numeric
select @count =count(*) from <table_name>
if @count >2 ....
END
Good luck for you.
Uyen Chi Uyen Chi
Software developer