@blocktrades options could be as follow:

• make it REP based, which means higher rep accounts gets lower PD time and lower rep will still have higher PD time. This will stimulate lower rep account to be more active and increase their rep. The best thing about it is that lower rep users are there since less time than high rep users and are more vulnerable for hacks and phishing atempts thus maintaining a higher PD would protect them more compared to high rep accounts who have been there since a while and are less vulnerable.
• Create a notifying messaging system, through email or through a notification on the different apps, to let users confirm through the click of a link in their inbox the PD or even let user confirm the PD through a onetime key passcode through a mobile message making it very very much harder for hackers to access sms on a device.