After collecting your dock seeds, spread on a baking tray and dehydrate in the sun or bake on low in the oven until dry and slightly toasted. Toasting longer will bring out the nuttiness of the seeds, but make sure you don't burn them!
Blend your seeds in a spice grinder or high speed blender. You can process into a fine powder, but I like to leave some of the seeds whole for a sturider, crunchier cracker.
Taste your dock flour. If it has a bitter aftertaste, put it in a jar with enough cold water to cover and leave for 24 hours, shaking occasionally. Usually this is all it takes to leach out the bitter tannins, but if necessary you can replace with fresh water and repeat the process. Strain through a cloth to get out the liquid.
In a large bowl, combine the dock flour, mushroom powder, and wheat flour. Add salt and any additional seasonings and mix together.
Add in water, a little at a time, until the mixture holds together but isn't overly sticky. Knead until well incorporated and form into a ball. Cover and let sit for 10 minutes.
Take half of your dough and lay out on a greased and floured baking sheet or parchment paper. Roll out into a thin rectangle, about 1/8 inch thick.
If the edges have cracked or formed holes, you can pinch them together or take additional dough to repair them. Cut the rectangle into whatever shape you'd like your final crackers to have.
Bake at 375 F for 15-20 minutes. Let cool completely before storing in an airtight container for up to a week.