coon problems

[bad moon]

i have been working with some yound dogs between one and two years. they are doing great on bobs and lions but i cant get them to take a thirty second old coon trail. they are on fire if i run it from a cage and they see it take off( even when the coon is far from sight like twenty thirty min head start) but if they never see it they wont run it. nothing changes at night, we can spot light one put the dogs rite on it and if they dont see it they wont chase. they all trail very well and dont need to sight chase by anymeans on big game. is there something i can do or are they dud dogs?