Seriously need a bolt lock on it pal. Not at the bottom tho, as then you have a fair bit of leverage ot rip it open. I would put it in the middle (i'm guesing you have standard sized gate - ala 6-7foot?) and make sure there is no way to get your hand through the gate to get at the bolt.

Least then the gate is more secure (might even put one at the bottom aswell to be safe - they only a fiver or less from B+Q....

With regard to the light, get it done, dispite what your missus says - afterall it's gonna be an aid to her anyway. Get a new style PIR for it and it's less sensitive to things like cats, fozes etc.