Guards
I could have included this as part of the 'monsters' or 'NPCs' subsection, but I think it merits its own passage. Guards probably don't receive or need as much personal development as other non-player characters, but they do require a bit of intelligence and planning if you want to use them in a suitably bastardly way.
- Patrol.
- Guards have patrol routes, taking in specific areas. They don't simply wander corridors randomly, unless they have received orders to do just that. Keep track of the time, and work out roughly where they'll be at any given moment. This will take a bit of practice but you'll get the hang of it eventually.
- Call for reinforcements.
- If the guards spot intruders, they do not immediately engage and fight to the death. The first thing they do is raise the alarm. Unless there's a sophisticated system in place for this, chances are that means sending a runner out to fetch more guards, while the rest of the squad stays behind to hold the area. The trick here is to make noise while doing it. Have him ring a handbell if he has one, while yelling "INTRUDERS!!!" or "ALARUM!!!". Double the probability of encounters from then on. Check for reinforcements every round.
- Use the terrain wisely.
- Guards know the area they're guarding. They know all the short-cuts, all the twists and turns. Have them catch the PCs in a pincer movement if they can. If the heroes get caught in a flanking action more than once, then it serves them right for not being careful.
- Use proper equipment.
- Are the guards assigned the job of patrolling long corridors or open spaces? Give them missile weapons or polearms. Do they have to patrol close, confined, claustrophobic areas? Short weapons are the order of the day.
- Tactical withdrawal.
- Sometimes discretion is the better part of valour. If the guards are having a hard time, have them fall back to a more defensible position. If they're outnumbered and reinforcements haven't arrived, then they should know well enough to try to beat a fighting retreat and regroup elsewhere.
- Take 'em alive!
- Sure, guards don't like intruders, but there's no reason to assume that four to six people are going to try to raid a complex on their own. There could be others, poised to counter-attack if the scouts don't get back. At any rate their leaders might want to question the PCs. To that extent they may try knocking characters out, or presenting overwhelming odds in order to force a surrender. Be creative.