The Dink Network

I'm trying to make a sprite move straight and diagonally, like brain 16 but without stopping. There doesn't seem to be one like that so I've made my own by using brain 6 and a script to make it run about and randomly change direction, but I can't work out a way to stop it running off screen without doing something ridiculously complicated. Any ideas?

Edit (30 seconds later): Maybe I could switch to and fro between brains 9 and 10... that would work. Unless someone has a better idea before I get around to testing?

Edit2: Tested and it works well enough