Trim the dark green and pink parts from watermelon rind. You could leave little bit of the pink on the rind.
Cut rind into 1-inch cubes and measure out 7 cups.
In a large bowl add 3 cups water and the salt. Stir it together until salt dissolves.
Place the rinds in the salted water. Cover with plastic wrap and place in the refrigerator for 24 hours.
The next day, drain the rinds and rinse well.
Add 4 cups of water to a stainless steel saucepan (or Dutch oven). Add the sugar, vinegar, cinnamon, pickling spices, and lemon slices. Bring to a boil. Stir until the sugar dissolves. Add the rind and simmer for about 30 minutes, until the rind is tender and translucent.
Remove from heat. Cool completely (about 1 hour), stirring occasionally.
Using a slotted spoon, transfer rind to jars; cover with pickling liquid. Apply lids. Gently pack the hot rind into the jars, leaving 1/4 inch of space below the lip. Pour enough liquid into the jars to cover the rind.
Wipe rims with a clean, damp towel and screw lids on securely but not too tightly.
Process in boiling water bath for 10 minutes.
Carefully remove jars using tongs. Use potholders to tighten the lids. Place jars on a rack and let them cool. When they’ve cooled down, store them in the refrigerator for up to two weeks. Chill 24 hours before serving.