[cmonkey]

have riders use a polo mallet to dribble a ball through a slalom cone course, then at the end of the course provide an arc of cones to shoot at.

Place the cone in an arc about 15-20 feet from the end of the slalom, and have various spacings count for different points.

make the center pair of cones about 10 inches apart, and from each side (continuing the arc), increase the distance between cones, with the larger distances being lower in point value.

10, 15, 20, 25 & 30 inch gaps worth something like 15,10,5,3,2.

Now time the slalom, and when they shoot and score, deduct the shot points from the slalom time. the one with the lowest score wins!.

By keeping the cones in an arc, and using them as common for each scoring area, the contestant is guaranteed a score of at least two points, unless of course they shoot completely outside the goal zone.

No chance of collision, they'll be concentrating too much on a skill they've never tried.

For goal markers, get those 3-4 foot long green plant stakes that look like plastic rebar and paint them orange.
They're thin enough so that deflection won't be too big of a deal, and they're strong enough to use over and over, and they're easy to carry along.
For the slalom cones get the flat sport type, you can carry 20-30 in a bag with ease.