It is a **very **good idea to wear a holy medal. As a sacramental it is a powerful sign and indeed by the very act of wearing it one is in fact sending up a constant prayer to God.
Wearing such a sacramental also offers powerful protection. It is not magic. Its power lies in the **faith **of the wearer and the very fact of wearing it would likely signify faith.
Whatever medal you decide on, do have it **blessed **by a priest. I can recommend the medal of St Benedict as well as the Miraculous Medal and the Divine Mercy. There is a special blessing for the St Benedict medal and this should be used.
You might also consider wearing a scapular such as the Brown scapular. Sacramentals, especially when blessed are extremely effective and powerful as they carry behind them in their use and blessing the whole weight of the Church.
Personally I am never without a good supply of holy water, holy oil, blessed salt, blessed candles as well as scapulars and holy medals. Holy pictures and statues as well as crucifixes in the home are also highly desirable. Especially given the times in which we live.