ADHD spouse always failing at business ventures

My ADHD husband is always trying to start new business ventures.  He has spent so much time and money in our 7 year marriage (and before that his parents were constantly financing his ideas) and nothing has ever worked but he says he will keep trying because he's not a quitter.  The problem is he jumps into things without having enough money to back him up and eventually loses the business and his investment, because he can't support it while it's in its early stages.  This is a man who has a business degree, he should know better!  His latest venture is going to be quite costly and time consuming and we have no money to invest in it.  I can see a disaster waiting to happen if he can get his hands on enough money to get started.  Does anyone else have this problem?  And how do you handle it?  We fight so much because he has financially devastated us in the past yet doesn't see that he is going down the same path again and again.  I try to reason with him but he says he's the one with the business degree and I don't know what I'm talking about.  His mother has tried to discourage him too and he won't listen to either of us.  I feel like he has no common sense and that irritates me to no end.  Help!