Been there.
Done that.
Got the hat and the shirt.
If you click on the "life is good" at the bottom of this post you'll see a pipe and stone gate that weighs about thirteen hundred pounds and works just fine.
If you built the gate you're describing and only went down four feet, well, that would be comparable to slapping a Grizzly that thinks you're a threat.
Here's some options.
1. Consider looking for a source for commercial fire suppression system pipe. It's the same outside diameter as schedule forty but is usually schedule ten or lighter. Same appearance, intimidating, but a fraction of the weight.
2. Think about what I've had considerable success with at places like rental yards etc. That's a barrier that folds down and up not unlike a railroad crossing guard. The difference is the RR barrier is designed to break away when hit and mine are designed to not break, away or any other way.
The advantage of the folding barrier is your pivot post only has compression forces upon it and no lateral ones. Therefore it doesn't have to have as substantial a footing.
One of the biggest mistakes I see made on these arrangements is they're built like a tank and yet it only takes a pair of bolt cutters or a cheap fire extinguisher and a hammer to go through the lock.
So on your latching mechanism think smart. Use the lock only to hold a pin that takes all the abuse. Say like a deadbolt lock that engages your horizontal pipe when it's in a down position.
Good luck.
And don't forget the dummy cameras. That'll stop the ones that will steal your tractor because that's what they do for a living.