I am thinking if i change metal duct to flexi duct then rats may chew right. please advise

Some with metal wire mesh screen, some with stucco or plaster, some with wood, some with expanding foam sealent (but make sure to stuff the hole first with steel wool - rodents can not chew through that, they can through the foam)

It's just not worth it to me.This dog dug holes all over the yard, chewed sprinkler heads completely off, chewed ALL of the wires off the sprinkler valves/solenoids so that they all had to be completely replaced, scratched/chewed up an exterior door and door casing, and literally chewed through a brand new fence/gate I had recently built.

Just a few thousand more to lose...there was nothing really BIG this year, but the necessity of not biting off more than my business model can chew is very important.

I’m trying to restrict my attention and not try to bite off more than I can chew.

I think this has probably been chewed over quite well, but just in case it hasn't.. it depends on your goals. 

I've been researching real estate like mad for the past year or so, having already chewed my way through some of the more popular real estate books.

Fake leather is best for furniture - easy wipe down- if pet friendly then stay away from real leather... some dogs like the smell and want to chew on it.

Many tenants will clean up after their pets, but in my experience, often times they will leave a good amount of previously digested pet food on the ground - hopefully outside.You are right - it is a risk, and like i said, if you don't take that risk, you really limit your potential renter pool.Often times these repairs are minor like scratches on the door or chewed baseboards, but without the animal those scratches and the expenses wouldn't be there.  

They are big burly guys that smell like diesel fuel, drive jacked up 4x4s and chew tobacco for breakfast.