Attempt of strict reading and applying this rule encounter some difficultiesLidless Eye, Standard Rules, Playing and Drawing Cards, Placing A Card On-Guard wrote:The company decides to face the site's automatic-attack. If the on-guard card is a hazard creature keyed to the company's site or a hazard that can modify the automatic-attack, it may be revealed before the automatic-attack is resolved. If it is a hazard creature, it will attack after the automatic-attack is resolved.
There is no problem in situation when site has only one automatic-attack. Then entering a site by company is synonymous with decision of face automatic-attack.
However this mental leap* (The company decides to face the site's automatic-attack.) cannot be applied directly to next AA. Company (nor its controlling player) cannot decide whether to face or not to face next AA. This decision was taken before and now company is forced to face AA.
In such situations we have following possibilities of interpretation:
a) Scaling by "all" - The company decides to face the site's automatic-attack. is readed as "The company decides to enter a site and to face all the site's automatic-attacks". Hazard creature keyed to the company's site or a hazard that can modify the automatic-attack may be revealed only before first AA.
b) Scaling be "each" - The company decides to face the site's automatic-attack. is readed as "When company faces each of the site's automatic-attacks". Hazard creature keyed to the company's site or a hazard that can modify the automatic-attack may be revealed before of AA.
If "a" is true then next question is moment of defining the second AA in under-deeps. Some of hazards that can modify the automatic-attack affects only attacks of certain type. E.g The Moon is Dead affects only attacks of Undead. Assuming that second AA is defined just before it is faced, then there are no conditions for revealing The Moon is Dead if first AA is other type than Undead.
Summing up, we have three options:
a1) The company decides to face the site's automatic-attack. is readed as "The company decides to enter a site and to face all the site's automatic-attacks". Second AA is defined just before it is faced. Hazard that can modify the automatic-attack of certain type cannot be revealed if type of first AA and type of attack that hazard is affecting does not math, event if second AA will be ultimately appropriate type. Creature revealed as on-guard will attack after resolving last of AAs.
a2) The company decides to face the site's automatic-attack. is readed as "The company decides to enter a site and to face all the site's automatic-attacks". Second AA is defined at the same time. Hazard that can modify the automatic-attack of certain type can be revealed if any of AA is appropriate type. Creature revealed as on-guard will attack after resolving last of AAs.
b) The company decides to face the site's automatic-attack. is readed as "When company faces any of the site's automatic-attacks". Hazard that can modify the automatic-attack and creature may be revealed before each of AAs. Creature revealed as on-guard will attack after resolving each of AAs and before resolving of next AA.
In this variant moment of defining second AA (when company enters a site, or just before resolving second AA) does not affect timing of revealing on-guards.
*) I'm not quite sure if "mental leap" is equivalent of polish "skrót myślowy" (literally "shortcut in thinking").