Sorry, that should read "Buy" not "But".

I'd like to put a couple of those expanding trellis style gates on the front and back sliding doors for security purposes. I like the idea that they can be folded away so they don't obstruct the glass when they are opened. I see them on some shop fronts but I have no idea as to where they can be purchased. Anyone know?

yeap if any knows please post...I am looking as well...I had trellis doors with slam locks in another country and the idea is great, if anyone is looking for a buiness to get started

http://www.trellidor.co.za/

giddyup, start looking and talking to shops that build gates and security bars. My BIL has something very similar on his house in KK. I would guess that the security aspect would be determined by the strength of the bars and by the design of the upper and lower runners (think 'captive'), not like conventional 'lift out' sliding door and windows. Fit and finish will be important for looks.

I may well design, and have fabricated, something like this for my own new build.