Lidless Eye says:CRF, Turn Sequence, Site Phase, On-Guard Cards wrote:An on-guard card may be revealed when the company plays a resource that
potentially taps the site. The card must affect the company or a character in the
company that site phase. Note that this clarification is looser than the rule printed on
p.61 of the Unlimited Rules book
CRF Lure of Expedience entry is rather a clarification* than errata.The card will remain on that site until one of the following occurs:
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.
The company plays a card that potentially taps the site. If the on-guard card is a non-creature hazard, it may be revealed if it is a hazard that directly affects the company or a character in the company (e.g., a hazard that forces all characters to make a corruption check).
Otherwise, return the card to your hand at the end of the site phase.
*) buggy and uses sloppy wording in my opinion.