I use a Gerber Clip Lock. A Blackie Collins design(First Production Run 1985). It has a double edged and double searated blade of 3.5" and a OAL of 8". This,for me ,is perfect. The blade and the handle are integeral and the sheith is a composite material. There is nothing to rust or rot.
I agree that most of the dive shops that are in my area seem to be affraid to carry a quality dive knife. They are starting to carry the Ti blades now but they start at $225ish.
The USN tried out some of the Ti blades a long time ago(before they were fashionable) but found them to be too brittle. Then they tried the Dacor brand and finally settled on a US Divers supplied knife. To me,they were a POS also. The knives are somewhat like the compressors in that the USN has tried them all.
Four or five of us will dive on the USS Oriskiney at the end of this next week. Our water has warmed to 84deg. so it will be nice out in the deeper water.
I would caution also, that divers should wear their dive knife on their forearm vs. their calf. Inside,outside,point down,point up,as long as it is on your forearm. My choice is outside with point down. GET WET !! --------