Two-Under Plus Fishbein Defense to 4C/5C

The opponents open 4C.  The standard defense is natural overcalls, plus double as takeout.

An alternative structure could allow for more description, at the cost of converting the takeout double for penalties:

X = both majors, or one major and diamonds
4(5)D = takeout
4H/4S = natural one-suited

After the double, partner assumes both majors and shows prewference in the two-under method; bid 4H with heart preference or 4D with spade preference.  If doubler had both majors, we get to the right major.  If doubler had the other major and diamonds, he now bids 4H after 4D spade preference, or 4S afetr 4H heart preference, and Advancer picks.  If doubler had a major-diamond two-suiter and Advancer prefers his major, we play there, which is probably OK.

This method could also be used in the event of a call that is practically forcing.  For instance, after P-1NT-4C, we could assume that 4C will never be played undoubled, in which case pass is forcing and the risk of not doubling 4C is solved.  Similarly, 4C (or 5C) after a strong, forcing opening might be a good time for this defense.