scissor jack safety

[Rob2]

These AU falcons are a bugger to get up onto stands at the front, mine is anyway.
So I was thinking about scissor jacks, they are great and safe to change a wheel etc, but not if you want to work under the car on suspension etc.
Why, not strong enough or might unwind and lower the thingy ?
I have a very strong wind up model capable of supporting a couple of tonnes,
I could get another one and have two.
When they are wound up the long screw bolt protrudes out of the frame,
so if a nut was done up on that bolt back to the frame it could be wound up but not down.
A larger square plate could be welded to the base so that it will not tip.

Should be a safe cheap stand.

Your views.