Thanks for making this a new topic. I looked around before responding to make sure it wasn't already a resource on the forum, but I definitely think it needs to be one as the term shielding gets used a lot in the Wiccan/pagan literature but rarely is well-explained, probably because each individual has his/her own method.
I think the topic of shielding, as Blue pointed out, brings up the issue of the need for shielding, i.e., what is empathy or being empathic. And, yes, we could start a whole other thread on this, but I'll leave it up to admin to decide if this reply should be split out. I'm posting this because I'm still evolving my thinking on this and am interested in others' opinions and maybe what I say will give Quotensilence some food for thought.
I've changed my thinking a bit on my personal definitions of empathy and compassion since I started this path and have found that changing my emotional perspective can alleviate the need for me to attempt shielding in some situations. I originally equated empathy and compassion and felt I was strongly both compassionate and possibly empathic. Then I realized that, to me, empathy is really a problem of lack of appropriate emotional filters and boundaries. In other words, I lack the normal mechanism that would allow me to distinguish the emotion that is appropriately mine and that which comes from an outside source. One remedy would be to learn to create a shield to compensate for the lacking boundary. I've learned that's like treating the symptom and not addressing the root of the issue; this is probably where many of you empaths will disagree. I see the underlying cause of empathy as attachment. I feel the pain, sadness, or whatever emotion of others because I subconsciously somehow attach these emotions to my own situation, issues or life. I see true compassion, on the other hand, as the ability to react to another person's predicament or feeling from a place of love without any attachment to the self. I believe this is what the Buddha taught. If I am able to realize this in a situation and change my perspective to one of non-attachment, I no longer feel the discomfort associated with taking on emotions that do not belong to me. That's not to say, that is in any way an easy thing to do, but I feel that eventually if I practice changing my perspective, I no longer will have the need to shield. In the meantime, I do not deny that shields can be an effective strategy for dealing with the lack of the normal emotional filters.