I'm with bookbinder on this. If you can seal round up in, it works a treat. Alternatively I've used Vitax SBK for years. Either way the trick is to drill or cut deep as you can into the stump and keep the wet out so that the stump killing ingredient can do what it says on the tin. Then when its dead you need to get the water in to rot it away. Or you can dig it out if you need to lose a couple of stone!
As for modeller you need to find someone with a chain saw, chop the stump to ground level then drill or cut to get the moisture in so that the wood rots. At the rate you are going your kids will be wondering what to do with the stump when they are old!