If you are planning to keep more than a puffer in a tank, the tank should be structurally complex, lots of decoration. A tank with a boulder all by itself in the middle of the tank is not a structurally complex tank. You have to be extra careful when you aquascape for a puffer tank.
Not many plants can be kept as puffers will damage them in search of food. For a freshwater tank, it is recommended that plants with thick and strong leaves and stems be kept only. In a brackish tank, certain plants like Java Fern and Java Moss can be kept for puffers will not touch these plants. Another solution is plastic plants which will last virtually forever but they will only serve as decoration and provide hiding for you puffer and will not aid biological filtering unllike life plants.
Now for the rockwork. Many forms of rocks are available, you can use boulders, lava rock, petrified wood and ect. If you plan to use lava rock, only buy lava rock that do not have sharp edges or you can smooth them down your self. Ensure that your rockwork is smooth so that it does not injure yout puffer. For a brackish tank, you can use dead corals as it will raise the water hardness(gH) and pH.
For substrate, ideally a fine sort of gravel should be used. Puffers spend their time in the gravel resting. Sharp gravel can injure your puffer. Once again, crushed gravel can be used for brackish tanks.
