Minelab Profind 35 - How Sensitive is it on Gold? 

What do you mean? Is it working good

No it froze up and even with new batteries, still wouldn’t work. Minelab are Awsome though and replaced it no questions asked. New one has been going strong for a few months now.

Cointector The 35 is water proof to 3m, so should meet your needs

Sounds good 👌

You can turn its sensitivity down to where it will only indicate when in contact.

Any metal detector detects metal........diamonds are NOT made from metal so the answer is NO

what a knob

You can change the sensativity to many different levels, it's very useful.