How many times has a property been vandalized or broken into and things have been stolen? One house they bought they found a homeless guy living there and chased him out. Then someone broken in and stole tools. The put in a camera that did not catch anyone. At another house someone threw a party and destroyed the house, then later the water heater was stolen costing them a thousand dollars
Looked online an in CA a security guard would earn about $30,000 a year. I guess that works to about $120 a night. If the projects take an average of 45 days to complete then that comes to $5400. That is assuming you are hiring the guard directly. If you are using a service they will have fees on top of that but we will stick with the $5400. You would need to lose more than $5400 on each property due to theft and vandalism in order to break even on this. Including this season I see 65 episodes so that is 65 houses. That is a cost of $351,000 over the span of 5 years or so. They would be spending $70,000 a year on a security guard. Probably more because this calculation is just on the houses that are on the show. They handle more properties per year than what we see.
I doubt they lose that much a year on theft and vandalism. Plus, I would not be surprised if they carry some sort of insurance that helps them out. That would be a lot cheaper than $70,000 a year. If we are measuring by water headers, you can buy one at Home Depot in Anaheim for less than $500. Lets add $200 to get it install (which is probably too high) then that means you would need to have more than 100 water heaters stolen per year to justify the cost of the guard.
The real problem is with the houses where there are signs of squatters. Once a house gets known by the homeless as being abandoned, they tend to rotate in and out and might not notice it's been purchased since they'd probably try to get in there at night.
Property Brothers had the same problem with one house where it had been vacant for a while, and it got broken into twice during the remodel. After the first time they put in a security light which scared the person off only after they'd broken the window.
Still, in general, it would probably be more cost effective to just begin work and demo as quickly as possible to make it clear the house is no longer abandoned. A security guard would be very expensive, and the way Tarek reacts like every little expense is such a terrible tragedy, I don't see him being all that willing to take the expense.
I've only seen one episode where the house was vandalized, but until papers are passed, it's still the seller's home. If they're passing papers on Monday the 10th, it's not illegal to go in the house on Saturday the 8th and "party". I'm sure the law varies state-to-state as to when the cutoff point is, but unless Tarek owns the house, it's probably T.S.