pots of it on my terrace.
Rue is another insect repellent herb - but I think toxic to mammals so you would have to be careful where you put it.
I feed my 13 year old dalmatian glucosomine & it helps her arthritis a lot.
Lots of people feed garlic to dogs for a flea repellent but with care as it it toxic, bonds with haemoglobin so that it cannot carry oxygen - anemia is the result & sometimes death. (Same with onion)
Not sure if it would affect horses that way, and it seems to need quite large amounts to be dangerous.
cheers - Dalfyre