Use the apg utility to generate strong mnemonic passwords:

$ apg -st

Please enter some random data (only first 8 are significant)
(eg. your old password):>
Coydgoceuk6 (Coyd-goc-euk-SIX)
Caculpyep7 (Cac-ulp-yep-SEVEN)
otevDet6 (ot-ev-Det-SIX)
Jiwacwarj6 (Ji-wac-warj-SIX)
gurkOnRyet1 (gurk-On-Ryet-ONE)
EbTarIv0 (Eb-Tar-Iv-ZERO)