Safety Gates

We need one of these for our sliding door. It's always open but it leads onto our deck and there are steps immediately outside onto concrete. I have to stop my commando crawling lil houdini from getting out there.

Which brand/s fit a sliding door?

The ones I saw in the shop came with extensions but man it was expensive! The extensions alone were $40 and we would need 2 of them plus the gate to fit a sliding door. Rediculous!

I've seen older-style wooden ones in people's homes that fit sliding doors.  Maybe cruise TM for a bargain?  I ended up shelling out for ours (for a normal doorway, but sounds like the same kind you described), 'cause I couldn't find any cheap ones that were sturdy and opened. 

Could DH make one? Willie made the one over our front door, it's a panel of plywood that slides into runners and the landlord made the one on our back stairs, again out of plywood but on hinges.

Actually, could you not just get a piece of plywood cut the length of the fully open sliding door and then slot it into the tracks of the door?