you should consider storing an agent's max id in another table. ( the following is MS-SQL compliant.. your flavor may require something slightly different )

you can quickly create this table like so:

select agent,max(id) 
into agent_id
from tracker group by agent
[download]

and then, before running your insert, run a transactioned query to get and set the max id of an agent

begin tran
set nocount on
update agent_id
set ID = ID + 1 where Name = 'abc'
select ID from agent_id where Name = 'abc'
commit tran
[download]

this should ensure you have no ID collissions

HTH!

Update: I just read the auto-incremental part of your post... which pretty much squashes this reply. shame on me.