I divide things - needed maintenance, cosmetic, and structural additions.
Needed maintenance is not really an investment, but it is protecting your investment. A lot of needed maintenance won't give you any extra money when you sell the place, but it will stop it from being a ruin. Maintenance is not and investment. In my (non-US) tax system, maintenance on investment properties does not change the cash base of the investment property, but, like interest paid on the mortgage, it counts as outgoings.
Structural additions might include a new garage, pool, adding an extra bedroom onto the house, a shed... These definitely add value to the house - but whether you will get a monetary return for that added value depends upon what you have and what has been done. If you already have six bedrooms, adding a seventh probably won't give you extra monetary return, whereas changing a house from two to three bedrooms usually will. Similarly with beautiful bathroom and kitchen renovations. These are probably all investments - but the return from the investment varies. In my tax system, these changes DO change the cash base of the investment property, and are not counted as outgoings. Fences would be included in this.
Cosmetic changes can vary. New paint is obviously maintenance, but usually enhances the value of the property when it is sold. A new granite kitchen bench replacing the laminated bench is obviously an investment (as it is not maintaining something with like for like - it is replacing something with something quite different).