Hard enough heat-treated chain (with a good hardened, shielded padlock) will foil most smaller bolt cutters. It won't stop a torch or an abrasive cut-off-wheel, though.
Chaining any two wheels together will stop the tractor from being driven, but any dedicated tractor thief probably is bringing a trailer with them and may have a winch.
Think like a bank. Combine these three things:
1. Physical barrier rated to delay the theft attempt for some amount of time.
2. An alarm system that detects the start of such an attempt.
3. Armed response (or law enforcement response) to such alarm within such minimum time.
In other words, if the tractor is chained in your yard, and your dog barks at the intruder right away, and you go investigate with a 10-gauge within a minute or so, you will likely deter the theft.
Chaining any two wheels together will stop the tractor from being driven, but any dedicated tractor thief probably is bringing a trailer with them and may have a winch.
Think like a bank. Combine these three things:
1. Physical barrier rated to delay the theft attempt for some amount of time.
2. An alarm system that detects the start of such an attempt.
3. Armed response (or law enforcement response) to such alarm within such minimum time.
In other words, if the tractor is chained in your yard, and your dog barks at the intruder right away, and you go investigate with a 10-gauge within a minute or so, you will likely deter the theft.