Dear Chandru,
I don't know if you have read my previous posts:
About future plans:
1. What are you looking for in your next job?
2. How does this opportunity align with your ideal position? What do you view as opportunities and advantages, as well as risks and disadvantages, in joining us?
Probing on the above is one of the best ways to learn more from the person - what would make them stay for another couple of years - or what would make them leave.
Also, any candidate's "intention" is to stay for a good period, provided there is a good career path, opportunity to earn, be recognized, and reach higher positions with greater responsibilities.
I never deny that (do you?)
Now, you will have a fair amount of information on what the candidate is looking for, like their dream organization. The rest is left to how you treat them and keep up with the promises. The candidate can, in turn, ask you, "Hey, it's a perfect match of position and what I am looking for in terms of monetary aspects. Now tell me, how do I gauge that your definition of an excellent work environment is really what I am looking for?"
Do you have the right answer for that? So, I crawl back again to the statement "Treat them the right way to ensure that whatever the candidate mentioned during the interview remains true."
Find out about the future plans and goals during the interview discussion; you will get to know more. Learn the art of probing, see their past experiences, question them about why they left each organization... Learn the ART OF PROBING!
Good luck!