Control a Portal for consecutive days.
For a Portal to count towards an agent's Guardian medal, the agent must own the Portal and own at least one Resonator deployed on the Portal.
Each Portal owned by the agent has its own Longest Portal Held streak, which increases every 24 hours and resets when he or she loses ownership. If the agent owns a Portal but does not own one of its Resonators, the medal will be awarded as soon as the agent deploys a Resonator onto it.
Because using an allied Flip Card grants the agent ownership of the Portal and all of its Resonators, the newly-turned Portal will count towards his or her Guardian medal.
Suspending the Streak Edit
If the agent has no Resonators deployed on the Portal, but still maintains ownership of it, his or her Longest Portal Held streak is suspended. This can occur when the agent's Resonators are upgraded by friendly agents, or an enemy agent destroys his or her Resonators without completely neutralizing the Portal.
In this state, a Portal still counts its Longest Portal Held streak, but the stat won't be reflected on the agent's profile, nor count towards his or her Guardian medal. When the agent deploys another Resonator on the Portal, or upgrades an existing Resonator, the Portal's streak will resume, retroactively adding the days it was suspended.
Ending the Streak Edit
If the agent loses ownership of the Portal, such as through destruction or the use of a Flip Card, its Longest Portal Held counter will immediately reset. This means that friendly agents can nullify a Guardian streak by using the enemy Flip Card. Recapturing the Portal will restart its Longest Portal Held streak from zero days.
Guardian is often considered the most difficult medal to obtain, as it's the only medal which other players can sabotage. Earning Platinum or Black Guardian requires diligent planning, tight coordination with other agents, deep strategy, and luck.
Rigorously recharging and defending the Guardian is the core mandate of the medal. The agent must own the Portal Key and distribute copies to trusted friends, so it can be recharged at any time. The agent's notifications must be properly configured so he or she can respond immediately to an attack. Replacing its Shields after attacks is also his or her responsibility.
That said, recharging a Guardian too aggressively could give away its status to casual attackers. The savvy agent will give enemy attackers a chance to move on before recharging; smart opponents will notice that the Portal is being remotely recharged and simply flip it to conserve weapons and end the streak.
The best Guardian Portals are inconvenient to attack, but not overly so. Selecting candidates that are far from population centers reduces the chances of incidental attacks, but if the location is too obscure, enemies will notice it on Intel and travel to attack it. Selecting a nearly inaccessible Portal also increases the chances that an enemy agent will use it as an anchor in a Mega-Field project, and complicates replacing its Mods.
Guardian Portals should be kept low-profile, to discourage enemies from traveling to them. If the Guardian supports multiple Links or Control Fields, enemies will attack it to earn the AP rewards. If it's a high level, it will appear on Intel at lower zoom levels. If it's a prominent landmark or has an amusing name, enemy players may want its Key as a trophy. If high-level Heat Sinks or Multi-hacks are attached to it, enemies may assume it's being farmed for resources. Any of these could result in the incidental destruction of the Portal.
Some agents enjoy the challenge of identifying and destroying enemy Guardians, and protecting a Portal from these Guardian Killers or Assassins requires the highest levels of preparation. Agents should avoid attaching overly high-level Shields to their Guardians, and limit how often they recharge the Portals; enemies will regularly scan Intel for outliers. Agents can thwart simple Intel Scraping tools that compare Portal and Resonator ownership by capturing the Portal, allowing a teammate to upgrade the Resonator, and returning just before a medal threshold to redeploy a Resonator and restore the counter.
More advanced scraping tools like Cerebro will detect Portals nearing Guardian thresholds and dispatch dedicated agents to end the streak. The only countermeasure is to prepare numerous Guardian candidates across remote locations in multiple Regions three to six months before the area's most brutal weather season. While Guardian Killer groups are smart enough to launch attacks in advance, an agent assigned to destroy one of the Guardians may procrastinate and later be shut out by weather or circumstance.
Since every Portal owned by the agent counts towards his or her Guardian, medal hunters should prepare and maintain redundant Guardian Portals. Any agent of either side could flip a given Guardian incidentally or purposefully, ending the streak unless a backup Guardian was prepared contemporaneously.