Farm Barrier

An excellent physical barrier is a distance between farms. A perimeter fence with a lock is required on every farm to prevent unauthorized entry by humans, automobiles, and animals present.
To alert outside visitors, use adequate signage.

Litter management

Litter should be collected from areas with good sanitation.
Before usage, fumigant the litter and allow it to dry thoroughly.
When the litter is saturated and generating ammonia gas, it should be changed.


Farm workers hygiene protocol

Unique farm clothing would be provided and worn to work on a poultry farm in an ideal world.
Apparel that has been washed must be dried and ironed—an efficient method for eradicating any airborne infection.

Vaccination crews should not be let in unless they have changed into farm-provided clothing.
Before and after use on the farm, should dip boots in disinfectant.

Use Foot-Bath regularly

Make a foot-bath with an effective bacteria-killing detergent and
Have workers step into it before entering the poultry pen and out again.

And most importantly dealing with dead birds. Find more details here
https://poultryabc.com/7-ways-to-ensure-biosecurity-on-your-poultry/