When people talk about the Air Corps needing jets, it is rarely clear what role they feel needs to be fulfilled, e.g. advanced training, counter-insurgency, air defence, public display role, or support of Irish forces deployed abroad. There is plenty of types to choose from, but there needs to be a clear need. Don't get me wrong - I'd love to see the Air Corps with jets again, but given the costs and competing priorities, a strong case would have to be made.
What kind of security role do you have in mind? If it is air-to-air interception, you would need to be talking F-16 class equipment, with all of the support and air defence systems that would require in order to be effective. Somehow I don't think we are likely to see that happening here.