Some of my own thoughts...
1) Is it appropriate for non-Buddhists to use Buddhist statuary in their gardens?
a. I should think that Buddhists would be more than happy that non-Buddhists should deem it fit that they should have an attraction/regard to use Buddhist iconography in their dwellings.
b. it would reflect the level of knowledge, research and considerate behaviour on the owner's part when using religious iconography of others, especially when it isn't from one's own convictions, especially in some parts of the world where in one's neighbourhood, where such is taken seriously.
c. Are Buddhists Idol Worshippers?
d. In fact, a nice garden Buddha with all the natural surroundings is one conducive environment for reflection...
http://www.accesstoinsight.org/tipitaka ... .budd.html
"All conditioned things are impermanent" — when one sees this with wisdom, one turns away from suffering. This is the path to purification.
"All conditioned things are unsatisfactory" — when one sees this with wisdom, one turns away from suffering. This is the path to purification.
"All things are not-self" — when one sees this with wisdom, one turns away from suffering. This is the path to purification.
2) If there are circumstances in which such people could respectfully use Buddhist statuary in their gardens, are there guidelines for use, placement, care of the statuary, etc?
For a non-Buddhist, perhaps if it may be appropriate, to keep a simple regard and respect for what the iconography represents other than being utilised and maintained as a mere decor, and some find a Buddha statue inspiring in challenging life moments...
For a Buddhist, as how they are taught in their respective School/Tradition as to the appropriate practices in handling such iconography.
i. In one's residence, for the sake of aesthetics, most would display in a prominent area/accessible part of their garden where it can be seen and appreciated by all who come in the owner's residence, kinda like in a hotel, where the lobby is the first contact point to effect a good impression for the guests
ii. It would be nice and a norm in some places if the statue is placed on an elevated platform/area, above ground level or some who can afford it, within a grotto or even a glass/metal/earthenware casing for practical purposes of keeping the longevity of the statue against Nature's elements, insects, animals and etc.
iii. One's motivation, keep it simple and sincere, the beauty of the statue is oft seen through the actions of the owner (where & how it is placed and decorated), other than the size, model, color, carving detail of the statue per se...
Dependent on the type of statue, the appropriate type of care will ensue.
Perhaps, one other detail is that the cleaning tools/items are to be kept separated and exclusive, not out of ritualistic reasons but for the practical purposes of avoiding soiling, contaminating and compromising the quality of cleaning tools & statue with other household items. An example is like the same cloth used to wipe a car would not be used to wipe one's face or the residence interior or the broom used to sweep the inner residence is kept separate from the one used to sweep a garden area...