I have a combination tall fescue and bluegrass lawn. When the bermuda that comes in and the bent grass, like once every five to seven years, just kill it, water for a month, kill whatever comes up and then reseed before fall so it is up and rooted before the really cold weather. Sod is Ok on a small area but expensive on a large area. One caveat on sod is that most sod growers use a cocktail to kill off weeds. 2,4-D is one of those chemicals and it is a known carcinogen in some canine breeds. Since we have one of those breeds, we have to buy special untreated sod.
Getting a good pre-emergent down a couple times a year will help keep weeds and unwanted grasses down. The seeds come in on the wind. That reminds me it is time to do my lawn again before the winter POA starts to take off in a couple weeks.