Certified GKH Gardening Expert
You can plant determinate varieties, or even varieties such as the patio type Red Robin.
Or You could also use Plant growth regulators. Products like General Hydroponics Bush Load Decreases internodal length, but it can carry some toxicity if not given time to flush out of the plant's system. Sometimes up to 50 days, even.
You can also use something like New Millennium Nutrients Decision, which is not so toxic but can still shorten the overall stature of the plant.
The least toxic, and best method if you already have the plant established and can't get to these products... Is training the plants sideways. Make use of trellising and cutting the tops off of plants to force branching down the sides. As well as keeping it shorter, it can also improve the yield of the fruit. The trade off here is the time it takes for recovery after each cut. They can still attempt to bear fruit, but Won't really get going until they have had time to heal and settle. Hope this helps some.
Plant determinate or dwarf tomatoes.
You should plant bush type tomatos that only grow to 2 or 3 ft. or you can prune the tops off when they reach the desired height.