The Competition Rules, 2019 edition, rule 184.108.40.206 states, in part “… If a retaining strap is permanently attached to a holster or magazine pouch, it must be applied or closed prior to issuance of the “Standby” command.”
There seems to be some confusion about this particular rule and how it is interpreted with regard to various means of retention straps/devices. This rule has been in the book since at least the old 2001 Red covered book because it was the first USPSA/IPSC rule I ran afoul of at my very first match. I was using an Uncle Mike’s holster with a sewn on snap strap. I was advised I had to have the strap applied to start the stage or I could remove the strap. I immediately adjourned to the safety table and deployed my trusty pocket knife to remove said offending strap, depositing it in the trash bin and rejoined my squad.
Something to notice about that story: It took a tool to remove it. Thus, it would be considered permanently attached per 220.127.116.11. The same can be said for any of the other myriad retention devices available out there that might be described as a strap up to and including the flip up plastic/Kydex/whatever retention devices often found on duty holsters.
Note that this rule does NOT apply to locks as found on “race” holsters. For Open and Limited I use a Ghost Holster from about a decade ago. That holster has three retention positions, unlocked (but there is still some resistance…not much, but some), locked (but you can still draw through it) and “double-locked” (you might end up pulling your belt up into your armpits but the gun doesn’t come out). 18.104.22.168 does not apply to any of those modes because none of them are a “strap” or anything that can be construed into a strap.
So go ahead and use that hair band, bungie cord, Velcro strap, etc. as long as it is not permanently attached. I generally recommend that loop type things be attached to the belt so they draw less attention from ROs that might think it isn’t legal (it’s on the belt, not the holster) and, if properly placed, is less likely to foul the works during the draw. But feel free to do what works for you as long as it meets the requirements of the rule.
Note: Permanently attached Velcro hooks or loops (e.g. glued on) do not then make that strap permanently affixed. One side of the Velcro being attached is analogous to a threaded hole for a screw. Just because it is there doesn’t make it functional…takes the other piece(s) to be a functional unit.
There is also another form of retention with relation to holsters and allied equipment that often shows up at matches. These are the “Battle Belt” type rigs with straps going around the thighs to hold the belt in place. These are often not legal as they fall under 22.214.171.124 (heel of the butt of the gun is too low) and many also run afoul of 126.96.36.199 (tie-down rig). Note there are exceptions per 5.2.8 at the Level 1 matches for active duty military and law enforcement.
None of us want to drop our handgun during at match at any time so it is logical and reasonable that we might want some additional security. Just make sure it fits within the rules please.