So maybe you've run a few trails and you want to set one yourself? Its not so hard. Here are some tips and ideas.
Circle Location
Probably the most difficult thing to find in Manila is a decent place for the circle, so its often a good idea to start with that. The basic needs are enough room to park around 10-15 cars, and an area where we can have a few drinks and a circle after the run. In typhoon season, a covered area is a definite advantage. Maybe you have access to a carpark at work that isn't used at the weekends, or perhaps you've driven past an area which looks as though it might work. Sometimes you can find new areas looking at the satellite view of Google Maps. If you can't find one yourself ask one of the regular hashers for a suggestion, as they'll probably know which locations have been used recently and which haven't.
Research the Trail
Previously this was a case of knowing the area, or trudging around it until you knew it well enough to set a trail. Nowadays the internet has helped enormously. Look around the area on maps.google.com and openstreetmap.com (its useful to use more than one map as they have very different coverage in the Philippines). You're looking to set a trail of around 9-10km for the runners, and around 5-6km for the walkers. Particularly useful for this is the website mapmyrun.com, which, once you've set up a free account, will let you draw on the map and which will tell you how long the trail is. It will also let you drag points around on the map to get something which is about the right length.
After you've got the trail idea, its a good idea to print it out and go and walk the trail beforehand to check that you really can get down all the roads: maps change and don't always correspond to real life! Sometimes you find additional tracks and trails through areas not marked on the map, so be prepared to explore and adapt.
Marking the trail
When you're sure that the trail is all clear, its time to mark it. The best time to do this is immediately prior to running it, because sometimes the elements can destroy your trail: paper can get blown away and rain is no friend to chalk marks. Generally if its an urban trail you can do the marking with chalk. If there's lots of grassland, you will probably have to use shredded paper, or toilet paper to mark the trail. There's no such thing as a trail with too many marks, so be generous, especially at intersections. You may like to make marks on the ground and on walls as well: vertical surfaces will retain the marks for a bit longer when it starts to rain. As you approach each junction, try to find an object in the field of view of the runners approaching the junction and put your mark on that. Be aware that cars and pedestrians can obscure marks after you've laid them.
Here are some of the markings we commonly use at M3H3. Each hash has a different code, so these aren't the only way of marking a trail, but you can't go too far wrong with these. The basic marks are just arrows which indicate the general direction of the trail. Straight, left, right, ahead a bit and then right, across the road, etc.
Getting Clever.
Checks, False Trails and Runner/Walker splits are ways of slowing down the fast people, and letting the slower people catch up. This means everyone gets home at the same time, and everyone has done exactly the right amount of exercise. A Runner / Walker split will typically divert the walkers down a shortcut, so that their total distance is around 5-6km (one hour of walking). There may be one split or several, depending on your available options. If you have splits you'll probably need a co-hare to walk one route, while you walk the other.
Checks also slow down the fast people. When they come across a check mark (a circle with an X in the middle in this case), the first few people split up and check all the available routes - there may be 4 or 5. When a runner finds an arrow, they'll start shouting On-On, so that the rest of the runners know the correct way to go. Usually one of the runners will then mark the correct way at the checkmark. But sometimes they forget. There may be between 1 and 10 checks on a trail, depending on the sneakiness of the hare.
False trails are the sneakiest of all. The front-runners will be running along when suddenly all the arrows stop, and FT appears on a pavement or wall in front of them. At this point, they retrace their steps, looking for a side road or alternate route. A good hare will have indicated this by writing an arrow on the reverse of an object, so that its invisible to outgoing runners, but easily visible when they're retracing their steps.