i wonder if somebody could offer me advice about splitting a website

hi

i wonder if somebody could offer me advice about splitting a website?
do i need to go down a multisite route, or is there another option?

i have a client - a vet who has 2 sides to the business - pet and farm
they want the pet side to be the mainsite but when you click on 'farm' it takes you into another part of the site, same design, different menu, different header/footer, different content

what would be the best way to do it, do you think?

thanks