Hi Jason, Kimberly here from landscape solutions for you. Thank you for asking about your tree. There are a couple of thoughts that come to mind in identifying the problem. Is your properly line have any drainage issues? Sometimes if trees are shrubs are in the path of too much water, this could put them into shock, and potentially drown the root system. Check to see how your water flows going to your property line.
Have you been in drought or too much rain during a time period? This can also cause stress on trees.
With another tree dying in your backyard, you might consider getting your soil tested. This could tell you if your soil is missing any critical nutrients.
Your tree could also have a fungus or possibly the beginning of a disease. I would recommend to take a branch with some brown leaves to your nearest nursery or garden center. Have them look at it and explain the conditions. They may be able to identify the problem and recommend a solution.
Feel free to give more details of you property line and water flow, your rain totals, etc... and we can go from there.
I hope this information can put you into the right direction to save you tree. Thanks again for asking the question, and feel free anytime to ask a question. I hope you have had a great weekend.
Kimberly