Well.. there is low stress training, like training to a screen or tying down with string, or there is high stress training like topping, fimming, or super cropping.

It's pretty self explanatory as to which is the least harmful/stressful when done correctly. And honestly, if it's 4 feet already it's going to get even bigger in flower. The absolute only way to keep it below a set height is to train it. Topping will slow vertical growth temporarily, but it will just respond with multiple tops shooting up, presumably above your fence, when the plant recovers.