Valve leakage

I hear a lot of myths surrounding leakage.
There have been many times when I have been asked to design a system where the client wants to hold a load almost indefinitely (leak free).
Most sliding valves need some leakage for lubrication due to metal to metal contact. Poppet valves or seated valves are as good as the next particle of contamination that lodges under the seat. Soft seated valves can give better chance of success but are less available.
The all ports blocked CETOP valve can cause problems with creeping rams. P port being close to A&B with T ports on the far side will allow pressure to A&B and send the ram out. The only remedy is either install a new valve or change to a P to T and a PO check.
Also in the attempt to lock off a load (hydraulicaly) can be dangerous. Any oil passing over the piston and with no route to tank will cause pressure intensification that might be well above the maximum allowed.
I have never relied on valves being leak free and always play safe.
Love to hear your views
Bob