[Buddha-l] Tortoise mind?

[jkirk]

When one is able to withdraw his senses from their objects under any
circumstance, just as a tortoise withdraws its limbs into the shell - his
wisdom is firmly established.

 Bhagavad gita, 2.58.
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I suspect there are similar adages in the Pali canon to this one; or are 
there?
I wonder how one can accomplish withdrawing one's senses from objects.
If one holds to the idea of the inseparableness of mind and body, 
considering these to be aspects of one biological process, it wouldn't seem 
possible as stated in this adage from the Gita. Would it not be more helpful 
to observe what happens in the thought process when one's senses apprehend 
this or that object?  Or would this claimed withdrawal be an aspect of 
concentration instead of insight meditation?

Would this practice be related to preparing for warfare (as in the 
Mahabharata, where we find the Gita, and with Krishna advocating that 
kshatriyas must observe their warrior dharma, etc.).

The simile of the tortoise hints at maintaining a shell-like armor around 
one's persona, usually dubbed a socially dysfunctional defensive attitude by 
psychologists.

Any observations on any of this will be appreciated.
(No agenda here--just wondering.)

Joanna