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[H.G.Muller]

You could make the engine suspicious of branches that have a large number of (reversible) consecutive checks in them at the end. You could apply this at the last level where you still consider evations (e.g. in an check-evasion node of QS). Normally you would do a repetition test, by comparing hash key with that of previous nodes, upto the last reversible move. But you could also test the in-check variable of these nodes, and then multiply the evaluation by a factor < 1 depending on the number of checks. (E.g. 1 or 2 checks would probably not be significant, and still use factor 1, and for 3, 4, 5, ... checks you could use factors 0.6, 0.3, 0.1, ...)

This should hadly take any time, as check-evasion nodes will not be very common.

To improve reliability of hashing you could also keep a running count of the number of consecutive checks (i.e. set the in-check variable to that of two ply earlier + 1 when you are in check, and reset to 0 when not), and add a spoiler key to the hash key whenever the in-check is above 2.