Or did you mean:

• are on one tail,

• are on one's tail,

• are on ones tail,

• are on tail,

• are one tail,

• are one's tail,

• are ones tail,

• are tail,

• were on one tail,

• were on one's tail,

• were on ones tail,

• were on tail,

• were one tail,

• were one's tail,

• were ones tail,

• were tail.