A good ratio is 100 linear feet of silt fence per 10,000 square feet of area. Improper quantities have a direct relationship to silt fence failures. Installation refers to the proper installation of fabric in the soil, and the creation of optimum conditions for compaction once installed. Again, a silt fence improperly installed is a complete waste of money. Fabric needs to be embedded deep enough in the soil to prevent under-cutting.
Compaction refers to properly compacting the soil to prevent water-saturation, or piping.
Compaction is achieved with the proper moisture, soil conditions, and fabric placement allowing mechanical compaction to take place. Uncompacted soil washes under the fence quickly and makes the installation a complete waste of money. Support posts refers to properly supporting the fabric for the fence to detain 18 inches of sediment-laden water. There must be as much support post below ground as there is fabric above ground. If not, the leverage created by 18 inches of water and sediment will push over shallow posts.