Because of recent British politics, everybody is talking about the “backstop”. Is there a nice word to translate this into Esperanto? I think another way to say it could be a “safety net”. This seems to be how it is translated in French newspapers (filet de sécurité). However I’m not sure how to translate that either.
It is always tricky to translate words which are very specific to a given culture or situation, which might not be known to many potential speakers who will come across that particular term. Most non-European English speakers might not even understand what a backstop is, unless they have followed the UK news over the past few months.
My preference would thus be to use a more generally understandable term, like the safety net you mention, or add some more context such as Irish border safeguard. Obviously you cannot add enough context to fully understand the term, but it should signal to the hearer/reader that there is some history behind that word that they might be unaware of, and will have to ask about if they don't recognise the issue.
The worst case would be for someone to hear the term and not realise that it is in fact a specific term, rather than a general word; in that case they might think they know what you are talking about, but don't really. Even Irish border safeguard might sound too broad for that, so maybe Withdrawal Treaty Safety Net would be specific enough to avoid this. Not as snappy as backstop, but more helpful in a conversation without shared political references!
After all that, my suggestion would be limgarantio. That kind of expresses the essence of the backstop IMHO.
As Oliver has said, it is difficult to translate this word without explaining what it is, and that's probably how we should translate it, so that it actually makes sense.
"Backstop" would then be "garantio pri malferma limo inter Irlando kaj Nord-Irlando". "Asekuro pri malferma limo", "promeso pri malferma limo". To add it more firmly into the Brexit-context, "klaŭzo de Briteliro pri malferma limo inter Irlando kaj Nord-Irlando". Other alternatives to "klaŭzo" are "speciala rezervo, kondiĉo, interkonsento", depending on what we're referring to.
I think this is one of the cases where we can't translate the word without adding in the context, which is why I expanded on the answer by Oliver in order to clarify the other alternatives without having to read through the comments.