Cutting of 1/8 inch of the blossom end (the opposite from the stem end),
Brining the cucumbers, and
if you do not remove the blossom end, add 2 grape leaves to every jar (I kid you not, they have something in them that makes the pickles crunchier, by neutralizing the enzyme in the blossom end that makes the cukes soft).
Cold packing your cucumbers also helps with keeping them crisp.
Soak cucumbers in ice water for 4 – 5 hours prior to pickling.
Alum may be safely used to firm fermented pickles. Alum does not improve the firmness of quick – process pickles.
The calcium in lime may improve pickle firmness. If you choose to use lime, purchase food-grade pickling lime, DO NOT USE AGRICULTURAL OR BURNT LIME. Food-grade lime may be used as lime-water solution for soaking fresh cucumbers 12 to 24 hours before pickling them. Excess lime absorbed by the cucumbers must be removed to make safe pickles. To remove excess lime, drain the lime-water solution, rinse, and then resoak the cucumbers in fresh water for 1 hour. Repeat the rinsing and soaking steps two more times.

You don’t have to do all of these but any try one or more of these steps and you should notice an improvement.

http://a-homesteading-neophyte.blogspot.com/2009/08/why-i-think-my-pickles-gone-soft.html