I'm not trying to be alarmist......but: When Sal was injured by his falling gate, I considered it a bizarre incident.....not the sort of thing you'd think would happen.
In yesterday's Thai Rath newspaper, front page, there's a photo and short story of a 41 year-old Korat resident who died when his steel gate (not all that big judging from the photo) slipped off it's rail and crushed him.

I remember when we lived downtown in a rental, after a month or two of straining to open the gate because of bad rollers, the landlady had them replaced. We were used to heaving open the gate....but with the new rollers, the gate slid open with ease and crashed against its barrier panel. It never skipped off the rail, but now I'm wondering if maybe that's what's causing these gates to come crashing down.

Food for thought.

Yes, both me and the wife have been extremely careful, since Sal's accident, opening and closing our gate, which is about 7 feet high and probably weighs half a ton.
We push it open from the end and pull it close from the same end.

Buy an electric gate opener, we bought one for about 35,000 bht, our gate is 5M long and at it's highest 3M tall, made of tubular steel. The opener came with a rotating light as a opening/closing warning (which i have disconnected, bloody annoying at night) and 3 remote units. A couple of the local likely lads fitted it and I did the electrics so they're not too fancy to install