If you want a visual OB, survey stakes work well painted white or yellow. If the basket is right near the path, I would seriously consider moving the basket.
As for general improvements, signage, score cards, tees, trash cleanup are all rather inexpensive. Signage is probably the most expensive depending on how you do it.
Hands down the best "improvement" would be to add additional sleeves for alternate placements, there by eliminating any potential safety conflicts and may eliminate the need for OB or Mandos.