"Tangg
ól" is "defend" although I don't think we use the root word alone except when it is used as someone's name (though I have never encountered anyone with that name) or nickname. Thinking along with @adrian313, it might be possible to use "tanggol" to mean "protection" too if you can make the same substitution in English.
The Tagalog word for "lawyer" is "m
ánanangg
ól" or "tagap
ágtangg
ól (the one who defends)".
I guess only a linguist may be able to address your need for an etymological explanation of the word. However, checking with Google Translate, it means "hedge" in Javanese, and "tanggul" in Indonesian is "embankment, dike, levee". The meanings appear to be related.
"Protection" is more of "sangga (parry a blow)" in Tagalog, but I also don't think that we use that root word just by itself. "Panangg
á (pang-sangga)" is "shield" in Tagalog.