You can't contain an organization that is running roughshod through that much territory, causing that much havoc, displacing that many people, killing that many innocents, enslaving that many women. The goal has to be to dismantle them.
When Obama was asked what's needed to really destroy ISIL, not just push back - NATO Summit Press Conference (9 September 2014)
Remarks by President Obama at NATO Summit Press Conference | whitehouse.gov[obamawhitehouse.archives.gov]