There's only one reason why your lawn ends up with moss garden. It's simply because moss is allowed to grow in your lawn.
Unless the cultural conditions for the lawn are optimized, the moss will always come back. Chemical removal only decreases the volume of moss temporarily, as it will not kill all the spores in the soil. In addition, power-raking the moss may worsen the problem because it will spread the spores to the entire lawn.
In order to prevent the moss problem in your lawn, it's very important to find the cause(s) and fix the fundamental problem(s). In other words, if you do not fix the fundamental problem, your lawn will keep suffering from the moss. The most common causes are...
By testing (ie- soil test) and/or analyzing the conditions, you may be able to identify one or more problems. There's always a way to fix any problem; therefore, you do not have to spent a lot of money on sodding every year!