How would you say "must" as in "Pet rabbits must be constantly looking for a way to escape."?

Question

On a forum, I said:

But can rabbits actually love humans? I doubt it. Think about it, they are prey animals. They must be constantly looking for a way to escape.

I was wondering, how would you say that in Latin? My attempt would be:

Si vultis habere animal quod simile feli est sed non edit carnem, acquiratis cuniculum. Credatis, nos habemus cuniculum.

Sed possuntne cuniculi vere amare homines? Dubito id. Cogites de eo, cuniculi sunt praedae. Ii debent semper sciscere modum fugii.

However, I'd guess that "debent" is not the right word to use here. So, which word is?

Answer 1

You are right that debere does not seem appropriate, as it usually stands for a moral or legal obligation. It is easy to remember if you know that the English word debt comes from debere (more directly from the participle debitum): Someone who owes a debt "must" pay it back, but alas, not in the sense that we can reliably expect him to actually do it.

What you seem to be saying, instead, is that even if we cannot directly perceive that the rabbits are plotting their escape, and cannot read their minds, we can still be sure it must be so, and for that I would simply say:

Sine dubio perpetuo facultatem fugiendi quaerunt.

Note that, while refugium exists, fugium doesn't really – fuga is the usual noun (or you can use a gerund like I did, or a relative clause in the subjunctive, e.g., quomodo fugiant). Aside from that, your text is straight from Calque Central as usual, but I want to stick to the question that was asked ;-)

Answer 2

I think that debeo works fine here. See Lewis and Short; debeo means to be bound (among other things), either by duty or by nature.

That said, there are indeed other ways to say this. Necesse est +infinitive, and oportet +infinitive. Oportet cuniculum semper sciscere modum fugii. Perhaps one of these might suit you better.