QuickBooks - like most accounting/financial tools - is a Garbage In/Garbage Out scenario. 

If the property is bleeding money every year from repairs, maintenance, or turn over you'll never get ahead.You can tap equity with a HELOC (challenging right now), cash-out refinance into a new loan (much higher rates), 1031 exchange, or sell (tax hit) but the numbers and property condition need to guide this decision.

Here's an out of the box strategy that I used to learn about real estate investing as quickly as possible, was to get my real estate license and start working with investors and property management companies. 

The question I have is have any of you rented out a property with a pool and if so what safeguards should I have in place to protect my myself?

On a 5% cap building, every extra dollar of NOI equals $20 in value, so you should squeeze out as much as you possible can.

But you'd always want to talk to the city right away (or county) and find out the development standards for the zoning that the lot is in (what are the setbacks, height limit, min lot size, etc).

Curbio may be able to help out.

Would it negativly affect my mortgage, or do I need to notify my lender at all to build the second home on the lot and then figure out the lot split later if it's necessary for renting or selling the new or original home? 

These neighborhoods are usually less risky than C Class areas, but showing solid comps, market trends, and your plan for value-add improvements will boost lender confidence.If you need any help with financing options, structuring deals, or putting together proposals, feel free to reach out→ I'd be happy to assist!

I believe in the power of networking and sharing knowledge, and I’m eager to connect with fellow investors to explore potential collaborations and opportunities.Feel free to reach out if you’d like to chat or meet up!