Personally I think if I had more than 5 DNF is a row I would od something, add a hint , make something more obvious etc, or treble check you haven't broken any rules by placing the cache somewhere it should not be.
Yes we like a challenge , but what is the point in placing a cache that no-one can find?
If I were looking after 10 DNF's in a row I would not even bother - we only after all have your word there is a cache there!!!!!
AS a CO I get satisfaction out of people finding my caches not logging DNF's
Saying all that if the cache is genuinely there and I lived in Reading again , i'd be in the location till I found it!