It is forbidden to speak lashon hara (gossip) about those who have passed away, and in fact there is a centuries-old cherem in place against those who do speak lashon hara about them. This is despite the fact that obviously someone who has passed away cannot be upset by what was said about him. This prohibition is mentioned in the Chofetz Chaim as well as in the Shulchan Aruch (Orach Chaim 466:3). The Mordechai writes that a person who is guilty of such a sin must go to the grave of the deceased to ask for forgiveness.
It is also prohibited to speak negatively about the Land of Israel – whether about its weather, produce, inhabitants, and so on. This appears to be (one aspect of) the sin of the spies, who spoke badly about the land of Israel itself. (See gemara Arachin 15a, and Avot de Rabbi Nattan 19:3).
It is very surprising that the Chofetz Chaim neglected to mention this prohibition. One possible explanation is that his whole sefer was intended to correct the type of negative speech that was prevalent in his times. It could be that the Jews of Europe felt so positively towards Eretz Yisrael that nobody spoke lashon hara about it at all, and so there was no need to include it in his sefer!
One may not speak negatively about the possessions of others, something which might commonly take place between competing store owners or producers. It would be lashon hara min HaTorah to disparage a competitor’s wares (being sold) or skills (for services being offered).
One might call a skilled workman to the house to repair something or do renovations. Sadly, it is common for such a person to disparage the work done by a competing workman whose work he is now coming to fix or improve on.
Therefore, one should not tell the workman which of his competitors had been there previously (and in the eyes of the current workman had done a terrible job) – for this may well lead him to speak lashon hara about the previous workman’s efforts and skills. (This is probably lifnei iver (placing a stumbling block before the blind) as well, for by bringing up the subject of the previous workman and his identity one would be causing the current workman to speak negatively towards him.) When one speaks negatively about the possessions of another, it is considered as if the lashon hara was spoken about the person himself, not just his possessions. (Chofetz Chaim 5:7, Be’er Mayim Chaim 8)