彼がやることをしっかり警戒したほうがいいですよ。

he; him; his; boyfriend

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to do; to undertake; to perform; to play (a game); to study; to send; to dispatch; to despatch; to put; to move; to turn (one's head, glance, etc.); to give (esp. to someone of equal or lower status); to let have; to present; to bestow; to confer; to make (a vehicle) go faster; to run (a business); to keep; to be engaged in; to practice (law, medicine, etc.); to practise; to have (food, drink, etc.); to eat; to drink; to smoke; to hold (a performance); to perform; to show; to ease (one's mind); to harm; to injure; to kill; to have sex with; to live; to get by; to get along; to do ... completely; to do ... broadly; to do ... to a great distance; to do ... for (someone of equal or lower status); to do ... to (sometimes with negative nuance); to make active efforts to ...

thing; matter; incident; occurrence; event; something serious; trouble; crisis; circumstances; situation; state of affairs; work; business; affair; after an inflectable word, creates a noun phrase indicating something the speaker does not feel close to; nominalizing suffix; pretending to ...; playing make-believe ...; alias; aka; nickname; alternative name; also known as

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

tightly (holding on); firmly; securely; strongly (built); solidly; sturdily; steadily; properly; well; sufficiently; hard (working, etc.); fully; completely; reliably; dependably; levelheadedly; shrewdly; wisely; cleverly

vigilance; precaution; watch; lookout; alertness; to be vigilant; to be cautious; to guard (against)

point (of a sword, etc.); pointed verbal attack

good; excellent; fine; nice; pleasant; agreeable; sufficient (can be used to turn down an offer); ready; prepared; profitable (e.g. deal, business offer, etc.); beneficial; OK

be; is

indicates certainty, emphasis, contempt, request, etc.; used when calling out to someone; used to catch one's breath or get someone's attention; yo!