Depends on how much under? And the target weight factors in as well. If you are talking 3 or four pounds I would pay the forfeit. If they are dogs in the low to mid thirties a couple of pounds is a lot to ask. If you know without a doubt 40 is his best and ideal weight and he is at 38-39 12 hours before after an hour in he can be another pound or so lighter so 2 pounds at 12 hours out could be three or four by the hour mark. If he is biting shit in half and you are not packing a lunch that factors in as well. If you are planning on being there a while that factors too.
Just saying under at 12 hours leaves a lot of variables to try to factor in/figure out. Just playing the odds if you are off at 12 just pay the forfeit and be right next time. When one of these dogs are deemed 'good' and some even 'great' one of the similar characteristics of these dogs is that they have the God given ability and heart to over come the owner's shortcomings. The owner should always limit those shortcomings the best he can and put the dog in the best possible position to do well. EWO