1) Ateat 2) Beset 3) Bulldog 4) Dour 5) Firm 6) Harassed 7) Obdurate 8) Pertinacious 9) Stubborn 10) Tailed 11) Tenacious 12) Tireless 13) Unyielding 1) Bulldog 2) Dour 3) Followed around relentlessly 4) Followed tenaciously 5) Obstinately determined 6) Persistent in effort 7) Pertinacious 8) Resolved to be followed 9) Shadowed 10) Showed off 11) Stubborn 12) Stubbornly tenacious 13) Stubbornly unyielding 14) Tailed relentlessly 15) Tenacious 16) Totally tenacious 
• (a.) Sullenly obstinate; obstinately determined or persistent; as, dogged resolution; dogged work. • (a.) Sullen; morose. • (imp. & p. p.) of Dog
Dog'ged adjective [ Fron. Dog .] 1. Sullen; morose. [ Obsolete or R.] « The sulky spite of a temper naturally dogged .» Sir W. Scott. 2. Sullenly obstinate; obstinately determined or persistent; as, dogged resolution; dogged work. 
dour adjective stubbornly unyielding; `dogged persistence`; `dour determination`; `the most vocal and pertinacious of all the critics`; `a mind not gifted to discover truth but tenacious to hold it`- T.S.Eliot; `men tenacious of opinion`
persistent in effort; stubbornly tenacious: a dogged worker.
[Difficult words] stubbornly unyielding stubbornly unyielding[Intelligent words] stubbornly unyielding