I guess you could just keep borrowing more and more money to pay for the maintenance of their properties since that’s your only job. 

I have a rental property that is paid for and I want to borrow the equity out of it for any future investments. 

It would only work for a single family, not 2-4 unit with a non-owner occupied co-borrower.

While not all are willing to cover the land costs (that is considered the borrower's "skin in the game") some can help cover the land purchase if the deal falls within their guidelines.

Can you borrow against your 401k? 

So you get to borrow $46k for $300/mo and pay $57k to borrow it for a total of $103k. 

I generally don't like the idea of borrowing against a 401(k) for any reason mainly because of risk that the loan will be called due to something outside of your control like losing your job. 

Is there a rule or guideline you follow to balance taxes so you are claiming appropriately but not to your future borrowing power?

If I borrowed $1000 from you and I paid  you back in 30 years, that $1000 would not buy what it buys now.

So if you borrow money against your home right now, you're going to pull the cash out of it, and then the market's going to fall and the value of the home is going to drop during the down cycle because we're looking at it heading into a deep recession.