bec et ongles
bona fide
committedly
consistently
constantly
deafeningly
decidedly
decisively
determinedly
devotedly
earnestly
faithfully
firmly
fixedly
forcefully
forcibly
hammer and tongs
heart and soul
heartily
imperviously
impregnably
in all seriousness
in earnest
in good earnest
in good faith
inflexibly
intensely
invincibly
invulnerably
irresistibly
like a bulldog
like a leech
loudly
loyally
lustily
mightily
obstinately
perseveringly
persistently
powerfully
pungently
purposefully
relentlessly
resistantly
resolutely
resolvedly
responsibly
robustly
ruggedly
seriously