With collar bars or pins: Most people do not realize how short the bars need to be. The shortest commercial bar Ive seen is 1-7/8ths inches long from ball end to end. It is too long for my neck. I have a 1-5/8ths inch bar that just works for my neck which is about 17.5 inches. The arrangement is supposed to be closely clenched to hold the tie in place but I often see it done loosely which is wrong.
Never put the safety pin throught the eyelet holes it makes you look like you just got off a...well it looks bad. Additionally, collars made for the eyelet bar are not designed to take the encompassing tension of the safety pin, which will tend to curl or crumple the collar front improperly.
The saftey pin leaves a little mark which I hadnt noticed until reading these forums increased my over attention to controling my every part of my environment. If it really bothers you, then set aside a couple shirts for this duty. But worrying about the small remainder marks on the shirt collars falls under the category of "poverty of the mind" which will keep a person from ever looking comfortable or at home in their tailored clothes.
The preoccupation with thrift or rather preserving things in their newest state creates the stiffest form of dresser ala President Truman. Relaxed and well worn (though clean and in good repair to be sure) is the mark of sophistication. Again 1-3/4" is about the longest outside measurement one will need on the safety pin style unless dealing with an exceptionally thick tie or collar material.
One ties their tie as they would normally, then pinches the collar gently with two fingers of one hand right under the tie knot, using the other hand's fingers to pin the collar in place relatively evenly. The absence of perfection is part of the art.
The collars should either be a straight point (or rounded point) in at least a medium length or a club (rounded) collar. The collar blades must be angled closely enough together to make their gathering with the pin seem logical. Although there are many elements at work here, as a starting guideline, if you need to place the pin into the collar more than a quarter inch behind the collars stitching it is far too spread a collar to pin. If after being pinned the collar fights against or unhinges the pin then either the pin is too short or the collar is, again, too spread. Likewise, if you need to pin the collar in front of the stitching, rather than behind it, the collar may be way too close together or too big for your neck.
The best safety pins Ive seen that are generally available are at paul stuart which carries mostly costume or base metal versions. highlandpark.com also carries base metal versions but has a selection of 14k pins and eyelet bars. Bear in mind, i believe their eyelet bars to be too long but their 1-7/8ths" bar is the shortest Ive ever seen. I might get my own 1-5/8ths pin copied.http://www.highlandpark.com/us/lis-mens-Collar-Pins.htmhttp://www.jewelbasket.com/mens-shirt-collar-pins.html
carries some beautiful eyelet bars which are again too long but if youre going to do it anyway, these are quite nice. The heavy slide on pin looks interesting. Im not a proponent of clip on pins but that one is, if nothing else, well cast.