Defensive position mad character had about source of cash, indeed (3,4,6)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

FORT (defensive position) + HATTER (mad character) containing [about] ATM (source of cash). ‘The Hatter’ appears in both Lewis Carroll’s Alice books but he is never referred to as ‘The Mad Hatter’.  The definition and answer are both used for emphasis and in some contexts may be interchangeable.