Chimney cowl for mice prevention?

[puri]

Hi, what kind of chimney cowl is available to prevent mice from entering, given mice can squeeze through 6-7mm holes?
We have 3 gas chimneys in old vicortian semi we are looking to protect from mice entering.

Thanks

 

[datarebal]

They will probably get gassed

 

[big-all]

no expert but mice and rodents need a draw they need a food source to attract them to an area where they will go to the minimum effort to achieve food and lodgings then they will expand iff the food source will supports more family groups
iff you have no rodents then see no point off worrying about the extremes

but fully a guess based on my experiances