Rocks won't do this, but they can provide water to the soil by encouraging dew in the early mornings. And they're permanent, which after the initial expense can make them cheaper in the long run. Compost is decomposed organic matter. It smells like dirt, should have lots of beneficial fungi in it and a low level of nutrients. One inch of compost a year should provide all the nutrients your annual flowers and vegetables need.
Most gardeners use too many fertilizers.
You can either sheet compost or pile compost. Sheet composting is burying your organic matter in the soil or under your mulch and letting it breakdown in situ. Pile composting is probably what most people do. They make a big pile of organic matter and let it decompose. Pile composting can be further broken down in to two types.