@DanBarrett w/ AdwordsNerds can better attest to this w/ even more data... but we released a report on PPC effectiveness that monitored millions of searches and over 5k leads for motivated house sellers... and we can show w/ data that Google PPC (and Bing too) are producing a great ROI to attract new clients who weren't doing a brand search.

What is a common way I could monitor my numbers when it comes to making a deal for an AirBnB arbitrage? 

Not only would it shine a light on how California's legal system enables this but it might shame the DA, Mayor etc into doing something about it.I would also inform the CA Bar Assoc. and ask them to monitor the situation.

They are monitoring the driveway/entryway only.

Ultimately what happens is the tenant is setting up a grow op or meth lab and the intent is to relax the landlord to the point that they do not properly monitor the property.

Concerning Water Sub-meters: Older buildings typically do not have individual shut offs (individual shut offs allow water to just one apartment to be shut off) a/k/a non-segregated plumbing; When allowed by the regulatory agencies, (in nonsegregated plumbing) a meter is installed on the water supply to the hot water heater; The meter measures the amount hot water consumed, the tenant is billed for every 1 gallon measured (hot water) the tenant is also billed 2.75 gallons (cold not metered); This is called Ratio Billing.When ever possible full capture is more accurate and allows for better leak detection.Sub-metering for smaller properties: Usually a sub-metering service (Reading,Billing, and Collection a/k/a RBC) will require a minimum to service a property; Although a reasonable billing fee can be passed through to the tenant; Smaller properties say less than 5 units may not be economical.Regardless if you bill your tenants for W&S, installing sub-meters will allow the owner to personally monitor leaks, waste, and excessive usage (extra tenants not on the lease) by apartment.

Dont worry about it in the future, as ordinances change and theres no real way for they to catch or monitor the situation specifically. 

Also, we might eventually provide system monitoring and billing tools to the landlords, which would be pretty essential, and would only costs a small percentage of what they are billing, but other than that everything would be free for the landlords.

Do you charge for monitoring and maintaining vacant units?

Do you want to monitor your tenants renters policy or are you more interested in the ability to file a claim direct with the insurance carrier?