YOU SAID:

You can horse around with horses but horses cant horse around because they are horses

INTO JAPANESE

あなたは馬と一緒に馬を走らせることができますが、馬は馬であるため馬を馬に乗せることはできません

BACK INTO ENGLISH

You can run a horse with a horse, but you can't ride a horse because a horse is a horse

INTO JAPANESE

馬で馬を走らせることはできますが、馬は馬なので馬に乗ることはできません

BACK INTO ENGLISH

You can run a horse with a horse, but you can't ride a horse because a horse is a horse