I have to make a person to push the lawnmower on a lawnmower cake. I have tried twice with fondant and the arms keep falling off, and it is just a mess - body slumps etc. Please help! Should I do it in gumpaste instead, or get a mold and do it that way?

I make my figures out of gumpaste or modeling chocolate, and if they have to stand up, I generally make a frame of wire first, then build on that.

Can you use skewers to support the base and toothpicks through the arms? I don't think any medium will hold erect while it's drying.

You can make your figure from fondant with tylose powder or mix 50/50 fondant and gumpaste. What are you using to attach the arms and how are you trying to position them? If they are away from the body you need to use something to support them until they dry. Take a look at the 2nd cake in my gallery (Nursing Graduation cake) I have her arm extended holding a diploma. It is attached by putting a piece of toothpick in the shoulder of the figure and attaching the arm to the toothpick and body with a little edible glue. Then I used support underneath the arm until everything was good and dry. If your figure is going to be pushing a lawn mower, the mower will help support the arms.