What if I bundle a project that I spent a lot of money on into a capital asset, my example being a retaining wall & garden installment, and utilize a depreciation cycle? That way I would at least get some return the following years.

If it is an improvement, that is fine.
The IRS indicates what constitutes a real property capital improvement as follows:
• Fixing a defect or design flaw
• Creating an addition, physical enlargement or expansion
• Creating an increase in capacity, productivity or efficiency
• Rebuilding property after the end of its economic useful life
• Replacing a major component or structural part of the property
Adapting property to a new or different use

Ok perfect! The primary driver for my question was that my smoke alarms are failing, they're 14 years old and should be replaced every 10 years. I wanted to upgrade them all to smart smoke & monoxide alarms for about $1,000.

Does TurboTax or IRS follow a specific depreciation cycle or do I manually indicate "10-Year Depreciation for Smoke Alarm Replacement" somewhere?

Rental property tends to wear out faster than normal so sometimes the IRS gives you a break on it.
• 5-year property. This class includes computers and peripheral equipment, office machinery (typewriters, calculators, copiers, etc.), automobiles, and light trucks.
This class also includes appliances, carpeting, and furniture used in a residential rental real estate activity.
Depreciation is limited on automobiles and other property used for transportation; computers and related peripheral equipment; and property of a type generally used for entertainment, recreation, or amusement. See chapter 5 of Pub. 946.

Ah ok! Thank you!

This looks like MACRS and not straight-line. I work as an IT procurement & asset manager so I am starting to see similarities.

Much appreciated.

My pleasure.