The level of protection needed depends in part on how you are going to apply the sealant. Sealant can be brushed on, rolled on with a paint roller, or sprayed on. I have had best results with foam rollers from Home Depot. Spraying is the fastest by far, but is the hardest to control. Some sealants have color in them and will stain surfaces to which they are applied.
Sealants are also rough on plants.
While most plants won't be damaged by getting hit with wafting over-spray, direct hits can do real damage. Wax or oil. Be careful considering Linseed Oil based wood protectors. In our experience they attract quickly black mildew. Professional sealants, which are typically superior, are oil-based.