Welcome to FlyerTalk, Matthew.

The first thing you can do to help your father out is to get him to join FlyerTalk! If he has taught you everything about being a frequent traveler, then he will certainly be welcome here.

A challenge may be hard to find (as you have found out). He should apply for the Marriott Premier Visa card, which will give him a 15 night credit towards his elite status every year. Gold can be attained with only 35 nights with the Visa.