Termidor SC is only able to be purchased by licensed professionals in the state of NY. We do have a link to New York products that are permissible for us to ship.
Termidor SC should not be applied if the ground is below freezing, or it will not take hold. Also, as long as Termidor SC has time to dry and bind with the soil, the rain will not affect it. It is best to wait until you have a few days of no rain in the forecast so there is at least 24 - 36 hours time after you treat before it rains. After that it will hold quite well to rain and weather.
Termidor applied in a trench really helps to prevent pest that are traveling through the soil. It sounds like you will need to re trench since over 10 years and then spray around the foundation 1 foot up and out with Termidor. You may also want to use apply dust like Delta Dust into wall voids for the spiders and other pest.
If the footer is right below the dirt level, within 6 inches, and it comes out 12 inches, then you should make your trench out where the footer ends. In other words, instead of digging a 6 inch trench directly against the structure, you will move the trench away from the house where you can dig down past the footer. You should still treat the soil in between the trench and the house (where the soil sits on top of the footer) by just drenching the soil if you can.
You can either drill into the deck to get to the soil underneath, or you may need to remove the plank or two closest to the structure so be able to treat the soil.
Termidor SC can only be applied one foot up and one foot out directly around the exterior of a structure 2-4 times per year or in a trench for termites. It should NOT be applied indoors or to trees, plants or lawns.